Please add following code in your theme’s (child theme’s if you are using) functions.php

add_action( 'init', function(){
	if ( ! empty( $_GET['fepaction'] ) && function_exists( 'um_stories' ) ) {
		remove_action( 'wp_enqueue_scripts', array( um_stories(), 'add_scripts' ) );
	}
});

Also if you want you can ask them to load their script only pages where that plugin’s form is loaded. That plugin is loading their script in all pages.