add_filter( 'frm_submit_button_html', 'add_custom_html_to_submit_button', 10, 2 );
function add_custom_html_to_submit_button( $button, $args ) {
	$target_form_id = 220; // change 220 to the ID of the form
	if ( $target_form_id === (int) $args['form']->id ) {
		// put HTML before the submit button
		$button = 'content before the submit button' . $button;

		// put HTML after the submit button
		$button .= 'additional submit button HTML';
	}
	return $button;
}