How to set a class for the button?

Hi,

You can add this code to the file functions.php in the child theme folder or use Code Snippets plugin to run the code.

add_action( 'wp_footer', function() {
    ?>
    <script type="text/javascript">
        jQuery(document).ready(function($) {
            $('.rwmb-form-submit .rwmb-button').addClass('className'); // Add your class name
        });
    </script>
    <?php
}, 999 );

It will help you add class to the submit button of the form. Or you can style the submit button with the CSS selector .rwmb-form-submit .rwmb-button {}.