Update _EventStartDateUTC & _EventEndDateUTC meta of tribe events.

functions.php

<?php 

// update utc time for tribe events
function wpuf_update_event_details( $post_id, $form_id, $form_settings, $form_vars ) {
	if ( !empty( $post_id ) && !empty( $form_settings['post_type'] ) && $form_settings['post_type'] == 'tribe_events' ) {
		$eventStartDate = isset( $_POST['_EventStartDate'] ) ? $_POST['_EventStartDate'] : '';
		$eventEndDate = isset( $_POST['_EventEndDate'] ) ? $_POST['_EventEndDate'] : '';

		if ( !empty( $eventStartDate ) || !empty( $eventEndDate ) ) {
			update_post_meta( $post_id, '_EventStartDateUTC', $eventStartDate );
			update_post_meta( $post_id, '_EventEndDateUTC', $eventEndDate );
		}
	}
}

add_action( 'wpuf_add_post_after_insert', 'wpuf_update_event_details', 10, 4 );
add_action( 'wpuf_edit_post_after_update', 'wpuf_update_event_details', 10, 4 );