您需要使用按钮单击回调来获取用户密码。由于您的代码现在已经编写完成，密码将被设置为空字符串（或者创建时EditText字段中的任何内容）。
从这个开始：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_change_password);
    final EditText password = (EditText) findViewById(R.id.newPassword);
    Button submit = (Button) findViewById(R.id.submit);
    submit.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String pass = password.getText().toString();
        }
    });
}

设置按钮点击动作后，创建一个类示例来覆盖authenticationChallenge方法，然后将该类传递给相应的AWS类进行身份验证，如下所示：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_change_password);
    final EditText password = (EditText) findViewById(R.id.newPassword);
    Button submit = (Button) findViewById(R.id.submit);
    submit.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String pass = password.getText().toString();
            AuthenticationHandler h = new AuthenticationHandler() {
                @Override
                public void onSuccess(CognitoUserSession cognitoUserSession, CognitoDevice cognitoDevice) { }
                @Override
                public void getAuthenticationDetails(AuthenticationContinuation authenticationContinuation, String s) { }
                @Override
                public void getMFACode(MultiFactorAuthenticationContinuation multiFactorAuthenticationContinuation) { }
                @Override
                public void authenticationChallenge(ChallengeContinuation continuation) {
                    if ("NEW_PASSWORD_REQUIRED".equals(continuation.getChallengeName())) {
                        NewPasswordContinuation newPasswordContinuation = (NewPasswordContinuation) continuation;
                        newPasswordContinuation.setPassword(pass);
                        continuation.continueTask();
                    }
                }
                @Override
                public void onFailure(Exception e) { }
            };
            CognitoUserPool pool = new CognitoUserPool(getApplicationContext(), "poolId", "clientId", "clientSecret", Regions.US_WEST_2);
            pool.getUser("userId").getSession(h);
        }
    });
}