Hello @Ekpo0,
The guest booked what you had available, that is to stay, the night of the 10th.
There's not any way you can cancel it without penalties if that's the only reason.
There are circumstances under which hosts can cancel penalty free for instant book listings. These are outlined in the help article below. If some other aspect of the reservation falls under those you could try contacting Airbnb support to discuss it.
If you didn't want a checkout on the 11th you should've blocked the 10th so no one could either check in or stay through that date.
When thinking about blocking dates it can be more helpful to think in terms of nights rather than days. In this case the guest booked the night of the 10th. Blocking a date blocks its night but still allows stays on the previous night.
How do penalty free cancellations work for instant book hosts?
Steve.