Hello @Sahar20
Sorry I am rather confused by your post.
Can you try rephrasing why it is that you can't accept a booking from this guest?
Why do you need to be there for the guest to check out on Sunday? If you didn't want to accept a booking for the Sunday, then the date should have been blocked out in your calendar so the guest couldn't IB (if that's what they did)
If you want to cancel then you should do so as soon as possible to help the guest have the best chance to re-book. You will, most likely have cancellation penalties imposed as Airbnb takes host cancellations seriously.
Most guests know they can use the translate function on messaging, but if not, it's fairly easy as a host to hit the translate button to help you understand what the guest is saying.