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 {}.
.
