Register a template location with Event Organiser for your theme

eo-theme-direct.php

<?php
/**
 * Registers the directory "[child-theme-dir]/event-organiser" as a template location for
 * Event Organiser. EO will look there when looking for the plug-in template files (e.g. single-event.php, archive-event.php, etc )
 *
 */
function mytheme_register_eventorganiser_stack( $stacks ){

        //$stacks is an array of (absolute) directory paths. EO will look in the order 
        //in which they appear in the array

        //Add theme sub-directory to beginning of the array 
        array_unshift( $stacks, get_stylesheet_directory() . '/event-organiser' );

	return $stacks;
}
add_filter( 'eventorganiser_template_stack', 'mytheme_register_eventorganiser_stack' );

?>