Buyers cannot confirm delivery. To change the tracking number you still need to generate the original prepaid label.
Then go to the More Actions dropdown menu or View Order Details > Postage > Track Package > dropdown arrow and change the tracking. That needs to be done on a desktop browser.
If the buyer paid for the unused label it will be refunded to them automatically in 30 days.
If you cannot manage to change the tracking the payment will be released anyway in 14 days.