If this was a Simple Delivery transaction for the first label, then the buyer will receive the refund if it's now not going to be used.
If you purchased the label the ' old way' through eBay, find your label with this link . https://www.ebay.co.uk/ship/lmng/labels-history/seller-hub and to the left of the sales record there is a drop down menu under 'Actions' click on that , then click on 'Void Label'.
The refund will take between 5 - 21 days to process.
Now you will not have tracking , your payout from the sale will take a minimum of 14 days to be released.
@teddy-edward1962