You can't now mark the item as collected / delivered, as it was originally listed for postage.
Best way forward would be to cancel the item, with buyer's permission , so citing Buyer Requests to Cancel, this fully refunds the buyer and your seller performance is not affected.
Then, relist it as a collection item for the buyer to buy and pay again.
Once you deliver your item the buyer must hand over a collection code for you to scan as this is your only proof them of delivery / collection.
You can leave the matter as it is, just deliver it, but you'll have no proof that it was delivered, so in effect if a case for item not received was opened, you'd lose and have to refund. Your payout also, would be held for a minimum of 14 days.
@burr1982va
