You may need to contact eBay Customer Services to correct this return postage label, or reissue a correct label for you , I'm presuming you're returning for item not as described reason, so eBay will charge this cost to the seller's account.
This is the easiest and quickest way to contact eBay Customer Services, for a Call Back option.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
Lines open 8 a.m. - 10 p.m. on weekdays
9 a.m. - 6 p.m. on weekends.
Automated agents will be available on chat outside of the above hours.
I recommend contacting CS first thing in the morning as there's more chance of Dublin answering.
@danilis_1