<?php 

/*
 * This snippet assign event tags with event using custom event submission form -> https://pastebin.com/Nvz4t6ca
 * 
 * 1. create mu-plugins folder under wp-content/mu-plugins/function.php
 * 2. edit function.php and Save
 */
add_filter('em_event_save','custom_event_save',1,2);
function custom_event_save($result,$EM_Event){
	
	wp_set_object_terms($EM_Event->post_id, X, EM_TAXONOMY_CATEGORY); // replace X with your events category ID
	
	return $result;
}