Hello @Jimme2
As you know Airbnb's long term cancellation policy which your guest booked under allows for 30 days notice.
You could refuse to amend the booking. However if you do so the guest could still arrive on Jan 8 and cancel giving you a months notice.
Better he cancels now so you have a longer period to try and get replacement bookings.
Accepting longer term bookings on Airbnb is always a risk because of the cancellation policy.