Reverse order of Past Events in Tribe Events Calendar via https://gist.github.com/elimn/0be6c4cbcf80b3721c81

functions.php

<?php
function tribe_past_reverse_chronological ($post_object) {

	$past_ajax = (defined( 'DOING_AJAX' ) && DOING_AJAX && $_REQUEST['tribe_event_display'] === 'past') ? true : false;

	if(tribe_is_past() || $past_ajax) {
		$post_object = array_reverse($post_object);
	}

	return $post_object;
}
add_filter('the_posts', 'tribe_past_reverse_chronological', 100);