Hallöchen @Lisa7 and @Lindy0,
here I found a similar question:
https://community.airbnb.com/t5/New-to-Hosting/A-guest-wishes-to-change-their-date-but-have-not-canc...
About airbnb fees the guest needs to talk to airbnb directly. You as a host you can only help him by may be returning the money to him as soon you got it. But this I only would do if I had a chance for an other booking. If the booking is blocking the calender its unfair from my point not to get any money. So for you as a host you should focus on how to get the calender changed as the guest is definatly not comming this weekend and you are not free to take any other guests at the moment.
It also might be that the guest is contacting airbnb to make a change of his booking. Airbnb may do it, but (hopefully) ask you than if you are fine with not to take a cancelation fee for this booking.
Herzliche Grüße
Gritta