You cannot, all you can do is to leave feedback, but if this was for an item over £10 that will not release the seller's payment any quicker, and it will be held for 14 days.
Send the seller a message, that under this new system of payment when eBay tracking is slow to update, they need to contact eBay Customer Services provide the tracking number which shows delivery, and they will release the payout 2 days after the delivery date.
@wardam-31
