If they are circumstances outside of your control such as a serious illness, broken down boiler etc, you can cancel under airbnb's exceptional circumstances policy (details in their Help Centre.
You don't say what has happened so difficult to advise.
if you don't meeting their exceptional circumstances criteria, you will need to cancel and accept the penalties Airbnb impose on hosts, as they take host cancellations very seriously.
Hopefully you meet the criteria under their policy.