Assign blog_id using em_event_save filter

<?php


/*
 * $_REQUEST['blog_id'] -> you can add HTML <select name="blog_id">...</select > in
 * the template file at events-manager/templates/forms/event-editor.php
 */
add_filter('em_event_save','custom_event_save',1,2);
function custom_event_save($result,$EM_Event){

	if ( is_multisite() ){
		$EM_Event->blog_id = ( !empty($_REQUEST['blog_id']) ) ? $_REQUEST['blog_id']:get_current_blog_id();
	}

	return $result;
}