Luis B

Hello, I bought an item at a London airport duty free shop. I now want to return the item back to the UK for a refund. I will be sending it back by mail package from a country in the EU (I am not a UK resident) The store will accept the return and give me a full refund but all the eventual customs and taxes will have to be paid by me. Is this specific situation eligible for a Return Goods Relief (RGR)? If so, what would be the steps required to claim it, (documentation, things to do on the package, notify the carrier, etc.) ? Thank you