woocommerce_dropdown_variation_attribute_options_args.php

<?php
/**
 * Hook: woocommerce_dropdown_variation_attribute_options_args.
 * Modify the parameters for the variation attributes.
 */
function plugin_republic_dropdown_variation_attribute_options_args( $args ) {
  // Modify the $args HTML here
  return $args;
}
add_filter( 'woocommerce_dropdown_variation_attribute_options_args', 'plugin_republic_dropdown_variation_attribute_options_args', 10, 1 );