Navigation arrows on thumbnails for WooCommerce

Hi!

I’ve been trying to find a way to add some functionality to my WooCommerce thumbnails. I want to display navigation arrows on the thumbnails the same way as they appear on the large image.

I have found the spot to place the markup in “inspect element” in Chrome but I don’t know where to publish it in the files of my website.

This is how it looks now
https://imgur.com/k3DhCJ9
https://imgur.com/8J34AHH

And this is the way I want it to look like
https://imgur.com/THT8vB2
https://imgur.com/3BOkW1z

If anyone can advice me on where to place this line that would be great! –><ul class="flex-direction-nav"><li><a class="flex-prev" href="#">?</a></li><li><a class="flex-next" href="#">?</a></li></ul>

Thanks in advance!