Use a PC/ laptop and Chrome and not the app to do this and change your bank details here:
https://ppcapp.ebay.co.uk/myppc/wallet/list
If there is still an issue you may need to contact eBay Customer Services for them to assist you here:
This is the easiest and quicket 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.
@Anonymous