Reorder a WordPress custom post type archive page by the value of a meta field. Based on this SE answer: http://wordpress.stackexchange.com/a/48658/25300

reorder-cpt-archive.php

<?php
    function slug_order_archive_by_field( $query ) {
        //Only do if is main query fo a specific cpt's archive.
        //@TODO set cpt's name
        if ( $query->is_main_query() &&  is_post_type_archive( 'CPT_NAME' ) ) {
            //@TODO Set the name of the field we are ordering by
            $query->set( 'meta_key', 'FIELD_NAME' );
            //@TODO change order to DESC IF you want to go in reverse order
            $query->set( 'order', 'ASC' );
            //@TODO uncomment next line IF you want to sort by an integer instead of alphabetically
            //$query->set( 'orderby', 'meta_value_num' );
        }
    }
    add_action( 'pre_get_posts', 'slug_order_archive_by_field' );