Best way forward here, is to cancel the order citing Buyer Requests to Cancel , and relist it when the buyer is back home to receive the item. This then doesn't affect your seller performance.
You'll need to message the buyer of course explaining this, and that delaying posting would give you a black dispatch mark on your eBay account, eBay expect prompt posting after an item is purchased. You need their permission to cancel not to receive a defect on your account.
This sounds like a Simple Delivery transaction, here the buyer has paid for the postage, explain eBay will refund them for the unused postage label.
@tuesday12345
