Adds comment support to the download post type
<?php
/*
 * Plugin Name: Easy Digital Downloads - Enable Comments
 * Description: Adds comment support to the download post type
 * Author: Easy Digital Downloads
 * Author URI: https://easydigitaldownloads.com/
 * Version: 1.0
 */

function pw_edd_comments() {
	add_post_type_support( 'download', 'comments' );
}
add_action( 'init', 'pw_edd_comments', 999 );
To implement this snippet on your site, create a brand new, empty WordPress plugin and paste the above code inside.