If it happens again, ask them to check at usually un-used entrances at their house, with neighbors, and with the PO. Sometimes it will accidentally get delivered to the wrong address, or is sitting at the PO waiting for pick-up.
There isn't a way to change feedback. I don't leave it until a few days after the DC says the item was delivered, or I wait until the customer leaves it for me first or contacts me about any issues.