@Alok Marathe.请检查下面的代码为您的问题.有很多关于堆栈溢出的代码，为您提供了如何显示更多功能的想法.
他们会给予你的例子与工作，你需要只是实现这一点。
这里是堆栈溢出链接，你的代码在下面。
stack-overflow

jQuery(document).ready(function ($) {

    //this will execute on page load(to be more specific when document ready event occurs)
    if ($('.product-info-box').length > 2) {
        $('.product-info-box:gt(1)').hide();
        $('.showmore').show();
    }

    $('.showmore button').on('click', function () {
        //toggle elements with class that their index is bigger than 2
        $('.product-info-box:gt(1)').toggle();
        //change text of show more element just for demonstration purposes to this demo
        $(this).text() === 'Show less' ? $(this).text('Show more') : $(this).text('Show less');
    });

});

/* Just For Example No Need */
* {
    box-sizing: border-box;
}

body {
    margin: 0;
}

/* Your CSS */
#product-info {
    margin-top: 0;
    font-family: "Cinzel", serif;
    background: linear-gradient(0deg, rgba(123, 67, 151, 1) 0%, rgba(220, 36, 48, 1) 100%);
    align-items: center;
    height: initial;
    padding-top: 100px;
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    width: 100%;
}

/* FOR GUITAR */
#guitarbox {
    display: flex;
    float: right;
    justify-content: center;
    margin: 40px;
    border-radius: 20px;
    background-color: rgb(237, 244, 199);
    transition: 1s;
    border-radius: 20px;
}

#guitarbox:hover {
    background-color: #bebebe;
}

#guitarcontent {
    margin: 30px;
    padding-top: 20px;
}

#guitarbox img {
    border-radius: 0px 20px 20px 0px;
}

/* GUITAR END */

/* FOR KEYBOARD */
#keyboardbox {
    display: flex;
    float: right;
    justify-content: center;
    margin: 40px;
    border-radius: 20px;
    background-color: rgb(237, 244, 199);
    transition: 1s;
    border-radius: 20px;
}

#keyboardcontent {
    margin: 30px;
    padding-top: 20px;
}

#keyboardbox:hover {
    background-color: #bebebe;
}

#keyboardbox img {
    border-radius: 0px 20px 20px 0px;
}

/* KEYBOARD END */

/* FOR VIOLIN */
#violinbox {
    display: flex;
    float: right;
    justify-content: center;
    margin: 40px;
    border-radius: 20px;
    background-color: rgb(237, 244, 199);
    transition: 1s;
    border-radius: 20px;
}

#violinbox:hover {
    background-color: #bebebe;
}

#violincontent {
    margin: 30px;
    padding-top: 20px;
}

#violinbox img {
    margin-right: 0;
    border-radius: 0px 20px 20px 0px;
}

/* VIOLIN END */

/* FOR CELLO */
#cellobox {
    display: flex;
    float: right;
    justify-content: center;
    margin: 40px;
    border-radius: 20px;
    background-color: rgb(237, 244, 199);
    transition: 1s;
    border-radius: 20px;
}

#cellobox:hover {
    background-color: #bebebe;
}

#cellocontent {
    margin: 30px;
    padding-top: 20px;
}

#cellobox img {
    border-radius: 0px 20px 20px 0px;
}

/* CELLO END */

/* Custom CSS */

/* Fixed div height */
.product_info_scroll {
    
}

/*  Not Necessary */
.showmore {
    text-align: center;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<section id="product-info" class="product-info">
        <b>Here are the instruments that our brand serves: </b>
        <!-- This div for making fixed height of show content -->
        <div class="product_info_scroll">
            
            <div class="guitar product-info-box">
                <div id="guitarbox">
                    <div id="guitarcontent">
                        <h1>Guitar</h1>
                        <hr>
                        <p>
                            An electric guitar is a guitar that requires
                            external amplification in order to be heard at
                            typical performance volumes, unlike a standard
                            acoustic guitar. It uses one or more pickups to
                            convert the vibration of its strings into
                            electrical signals, which ultimately are
                            reproduced as sound by loudspeakers.
                        </p>
                    </div>
                    <div id="guitarimg">
                        <a href="https://en.wikipedia.org/wiki/Electric_guitar" target="_blank">
                            <img src="/images/electric-guitar.jpg" width="500px">
                        </a>
                    </div>
                </div>
            </div>
            <div class="keyboard product-info-box">
                <div id="keyboardbox">
                    <div id="keyboardcontent">
                        <h1>Keyboard</h1>
                        <hr>
                        <p>
                            A musical keyboard is the set of adjacent depressible
                            levers or keys on a musical instrument.
                            Keyboards typically contain keys for playing the
                            twelve notes of the Western musical scale, with a
                            combination of larger, longer keys and smaller,
                            shorter keys that repeats at the interval of an octave.
                        </p>
                    </div>
                    <div id="keyboardimg">
                        <a href="https://en.wikipedia.org/wiki/Musical_keyboard" target="_blank">
                            <img src="/images/keyboard2.png" width="500px">
                        </a>
                    </div>
                </div>
            </div>

            <div class="violin product-info-box">
                <div id="violinbox">
                    <div id="violincontent">
                        <h1>Violin</h1>
                        <hr>
                        <p>
                            The violin, sometimes known as a fiddle, is a
                            wooden chordophone (string instrument) in the
                            violin family. Most violins have a hollow wooden
                            body. It is the smallest and thus highest-pitched
                            instrument (soprano) in the family in regular use.
                        </p>
                    </div>
                    <div id="violinimg">
                        <a href="https://en.wikipedia.org/wiki/Violin" target="_blank">
                            <img src="/images/violin.jpg" width="500px">
                        </a>
                    </div>
                </div>
            </div>
            <div class="cello product-info-box">
                <div id="cellobox">
                    <div id="cellocontent">
                        <h1>Cello</h1>
                        <hr>
                        <p>
                            The cello (/ˈtʃɛloʊ/ CHEL-oh; plural celli or
                            cellos) or violoncello (/ˌvaɪələnˈtʃɛloʊ/ VY-ə-lən-CHEL-oh;
                            Italian pronunciation: [vjolonˈtʃɛllo]) is a
                            bowed (sometimes plucked and occasionally hit)
                            string instrument of the violin family.
                        </p>
                    </div>
                    <div id="celloimg">
                        <a href="https://en.wikipedia.org/wiki/Musical_keyboard" target="_blank">
                            <img src="/images/cello2.jpeg" width="500px">
                        </a>
                    </div>
                </div>
            </div>

        </div>

        <div class="showmore">
            <button type="button">Show More</button>
        </div>
    </section>