in this case you would use event handlers for the comboboxes, and then refresh the datagridview based on the selected values. Here's a basic outline of how you might implement this in C#:

First, you would want to handle the selection change event for both the cbSelectYear and cbSelectMonth comboboxes.

private void cbSelectYear_SelectedIndexChanged(object sender, EventArgs e)
{
    RefreshDataGridView();
}

private void cbSelectMonth_SelectedIndexChanged(object sender, EventArgs e)
{
    RefreshDataGridView();
}

Then you would implement the RefreshDataGridView method:

private void RefreshDataGridView()
{
    string selectedYear = cbSelectYear.SelectedItem.ToString();
    string selectedMonth = cbSelectMonth.SelectedItem.ToString();

    string query;

    if (selectedYear == "All" && selectedMonth == "All")
    {
        query = "SELECT * FROM TKDV";
    }
    else if (selectedYear != "All" && selectedMonth == "All")
    {
        query = $"SELECT * FROM TKDV WHERE YEAR(UsageTime) = {selectedYear}";
    }
    else if (selectedYear != "All" && selectedMonth != "All")
    {
        int monthIndex = DateTime.ParseExact(selectedMonth, "MMMM", CultureInfo.InvariantCulture).Month;
        query = $"SELECT * FROM TKDV WHERE YEAR(UsageTime) = {selectedYear} AND MONTH(UsageTime) = {monthIndex}";
    }
    
    // Rather use stored procedures
}

This is a simple example that might need to be adapted based on your specific needs. It assumes that the "All" option is represented as the string "All" in the comboboxes. Also, it assumes that the selectedMonth is the full name of the month, and that's why it is using DateTime.ParseExact to get the month index.