Hello Dionizio Find,
Please refer to our theme documentation here: https://www.8theme.com/documentation/docs/xstore-size-guide-on-product-page/ for instructions on how to proceed.
We have also prepared a video tutorial on our test site for your reference.
https://www.veed.io/view/af01e837-ae60-4310-858a-d7788b50310c?sharingWidget=true&panel=share
Best Regards,
8Theme’s Team