Variation to existing listing?

I am trying to add a variation (shoe size) to an existing listing created by someone else. Not sure why someone was able to create a listing with the same EAN. I have the proper brand approval in place with Amazon.

When I search by EAN, I check the add variation (size) box, fill all the necessary information, add a variation, add new pictures. It shows in my inventory. However it doesn’t show in the product page.

Any guidance, step by step tutorial, or recommendation to add a variation to an exist item created by 3rd party?