Goto AMD support website and follow the steps as given and if sending via courier or taking in person, do provide a copy of bill/take original with you and with all accessories it comes with.
It is inspirysis afaik who takes care of RMA.
Only if you have the registered email from zotac and bill. Otherwise warranty is 3yrs for 30 series zotac that extended warranty is only valid if registration was done within 28 days from buying the card