With so little information we're only guessing, but I assume that you're trying to buy a preprinted return label through eBay?
If eBay requires you to have a Paypal account to pay you can simply pack and post the item in the usual way, and pay at the Post Office.
Remember that the item remains your responsibility until delivered back to the seller, so don't forget to use recorded delivery or similar, and to use an insured service if the item has any value.
