You need to do this now only on the Seller Hub, try using a PC / laptop too, if presently using the app or mobile browser. Chrome and Firefox work best with eBay.
Click on link below to bring you to the Seller Hub:
https://www.ebay.co.uk/sh/ovw
go to Orders >> Awaiting Postage / Print Postage label, and then click the box on the left of the item.
https://www.ebay.co.uk/sh/ord/?filter=status:AWAITING_SHIPMENT
From the Postage tab above, use the drop down menu there, if the option to mark as collected is not there, then select Mark as Paid and Mark as Dispatched.
Dispatched is eBay's wording for a collected item.
