@Nancy489
I presume the guest has paid you direct to avoid booking fees, crafty so and so's are guests.
No way to give it to airbnb that I know of, you should have altered the booking at your end and the guest would have paid airbnb and the fees.
When you personally take money from a guest for extending a stay, the extended stay is not through airbnb.
2 choices, return his money and alter the booking from your reservations, they will then get a request to pay from airbnb but it will probably cost the guest more.
or just keep quiet and hope nothing goes wrong during the stay.