Example of how to change the 'Return to event list' used by the MER plugin to link to the page the user users to add the event to the cart,

example.php

<?php //Please do include the opening PHP tag if you already have one.

function tw_ee_mer_change_event_list_url_to_referer( $return_url ){
	if( !empty( $_SERVER[ 'HTTP_REFERER' ] ) ) {
		$return_url = $_SERVER[ 'HTTP_REFERER' ];
	}
	return $return_url;
}
add_filter( 'FHEE__EED_Multi_Event_Registration__set_definitions__events_list_url', 'tw_ee_mer_change_event_list_url_to_referer' );