Thank you for your inquiry, you can edit ssf-wp-xml.php and search for the following code:
$query=$wpdb->get_results("SELECT * FROM ".SSF_WP_TABLE." WHERE ssf_wp_store<>'' AND ssf_wp_longitude<>'' AND ssf_wp_longitude!='0' AND ssf_wp_latitude<>'' ORDER BY ssf_wp_store ASC", ARRAY_A);
and change it to:
$query=$wpdb->get_results("SELECT * FROM ".SSF_WP_TABLE." WHERE ssf_wp_store<>'' AND ssf_wp_longitude<>'' AND ssf_wp_longitude!='0' AND ssf_wp_latitude<>'' ORDER BY ssf_wp_zip ASC", ARRAY_A);