Visit the Manage Products screen and enter this GTIN to view that specific product detail record, and confirm that it’s the same product as the one you’re trying to import. You don’t have to take any additional steps, as the other items in the update file were successfully imported.
If you believe that the GTIN was previously assigned, and you have In Use products with the same GTIN, you will need to assign a new GTIN to one of the products, then communicate this new GTIN both internally and externally to your trading partners.