Filter the redirect URL for successful FES Submission Form submission
<?php
/*
 * Plugin Name: Easy Digital Downloads - Submission Form Redirect
 * Description: Filter the redirect URL for successful FES Submission Form submission
 * Author: Sean Davis
 * Author URI: https://easydigitaldownloads.com/
 * Version: 1.0
 */

function sd_fes_submission_redirect( $response, $post_id, $form_id ) {
	$response['redirect_to'] = 'http://SITEURL.com/';
	return $response;
}
add_filter( 'fes_add_post_redirect', 'sd_fes_submission_redirect', 10, 3 );
To implement this snippet on your site, create a brand new, empty WordPress plugin and paste the above code inside.