Using a PC / laptop and try Chrome that seems to be the best combo, you should be able to manually correct the tracking entered, where you marked the item as dispatched.
If not, you'll need to contact Customer Services, and they will correct this for you.
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 between 8 a.m. to 10 p.m. on weekdays.
9 a.m. to 6 p.m. on weekends.
I recommend contacting CS very first thing in the morning, when the lines first open, as there's more chance of Dublin answering.
@trac6z4p
