order-categories.php

<?php
/**
 * Filter select field.
 * 
 * Check if select field options are terms and then change orderby and order value.
 * This filter will work only with AnsPress 4.1.0
 */
function my_category_field_filter( $args, $form ) {
  if ( 'select' === $args['type'] && 'terms' === $args['options'] ) {
     $args['terms_args']['orderby'] = 'orderby';
     $args['terms_args']['order'] = 'DESC';
  }
  return $args;
}
add_filter( 'ap_before_prepare_field', 'my_category_field_filter', 10, 2 );