Add a new tab to the Frontend Submissions vendor dashboard menu.
<?php
/*
 * Plugin Name: Easy Digital Downloads - FES Login Form Redirect
 * Description: Add a new tab to the Frontend Submissions vendor dashboard menu.
 * Author: Easy Digital Downloads
 * Author URI: https://easydigitaldownloads.com/
 * Version: 1.0
 */

function custom_fes_login_redirect( $response, $userdata ) {
	$response['redirect_to'] = 'http://google.com/';
	return $response;
}
add_filter( 'fes_login_form_success_redirect', 'custom_fes_login_redirect', 10, 2 );
To implement this snippet on your site, create a brand new, empty WordPress plugin and paste the above code inside.