How to Update or Add a UPC/EAN or ISBN to an individual product in Shopify

In Shopify click on Products in the left navigation then the individual product you want to add a UPC to.

Scroll to the Inventory section

Add the UPC and click Save at the bottom of the page.

How to bulk add the UPC, EAN or ISBNto your Products in Shopify using a csv file

You can bulk update your products in Shopify using the instructions on the Shopify site:

You can check GTIN/UPC existence here