@Buffy20
A "change" request on a reservation can only be sumitted if the reservation is upcoming or active. After the official check-out time the reservation has finished. So how can you sent a "revised reservation" on an already completed reservation ?
Besides of that, i would not honour the extra night. You already have been there, cleaned the space.
So lock the doors and sent guest a message the reservation has ended (which the guest can also see for themself).
Let us know how this ends !