eBay sent me a pre paid postage label but when I took it to the post office they would not accept it so I had to purchase a new label but I can't change the tracking details on my sold item and I won't get paid until the item is delivered
You should be able to change the tracking via the More Actions dropdown menu but it needs to be done on a desktop browser. If you don't manage it the payment will be released anyway in 14 days.