You cannot now unfortunately.
Items listed for collection after being purchased and paid for, the buyer receives that all important 6 digit QR code.
This when given to the seller who scans or enters the numbers manually, is the only form for marking the item as collected , and to release the payout sooner.
You will not have this code as the item was listed as postage only, so will now need to wait 14 days before release of your payout.
If you are a new or returning seller, there may be a longer hold of 30 days.
@jacovandermerwe1971