@Hiroshi1, it's important to know if the guest has already arrived, or cancelled the reservation beforehand, and for how long was the reservation.
If the guest cancelled beforehand, you don't need to do anything. It's between the guest and AirBnB. (After all, AirBnB has his/her money, not you.)
Your guest will - or should be - refunded in accordance with your cancellation policy, which I see is 'strict'.
If the guest has already arrived, AirBnB will need to determine the refund - if any - on the basis of your cancellation policy.
I strongly urge you to read carefully through the list of links here so that you become familiar with how AirBnB operates.
https://community.airbnb.com/t5/General-Hosting/Community-Help-Guides/m-p/23100#U23100