Do you not have a purchase receipt/proof of purchase?
Won BSTRD.: if you received BSTRD. as an incentive from e.g. your employer or won it in a competition or the like, then you can enclose a document (letter or e-mail) as proof of warranty which shows that you received or won BSTRD.
Items that are required to be listed on this are: name of giver, name of receiver (owner), which model type (size + year), owner address, owner phone number and the date of purchase. This then serves as proof of purchase. You can register it online for warranty.
Received BSTRD. as a gift: to claim warranty, a copy of the proof of purchase is required (note: no debit card transaction). We can imagine you don't have one if you received your BSTRD. as a gift. Then request it from the giver anyway, so you can register you BSTRD. and make use of the warranty (if necessary).