/* Tribe, change related posts arguments */

Change_related.php

<?php

/* Tribe, change related posts arguments */
function tribe_modify_related_posts_args ( $args ) {

	$args['meta_key'] = '_EventStartDate';
	$args['orderby']  = 'meta_value';
	$args['order']    = 'ASC';

	return $args;
}

add_filter( 'tribe_related_posts_args', 'tribe_modify_related_posts_args' );