addtowishlist.php

<div class="yith-wcwl-add-button add-to-fav-custom">
  <a href="?add_to_wishlist=<?php echo $related_product->get_id(); ?>" rel="nofollow" data-product-id="<?php echo $related_product->get_id(); ?>" data-product-type="simple" data-original-product-id="<?php echo $related_product->get_id(); ?>" class="add_to_wishlist single_add_to_wishlist" data-title="Añadir a la lista de deseos">
    <i class="fa fa-heart-o"></i>
  </a>
</div>