Hi @Matz9 🙂
If you cancelled a guest stay then the days will stay blocked.
If you just turned down “a request to book” - Airbnb will automatically block the days as the system will assume that you can’t host those specific days. You can if that is the case reopen those days in the calendar section. Just click on the dates and make them bookable again. That is not the case if you cancelled an already confirmed booking as the blocking is part of the penalty for cancelling out on a guest. Hope that makes sense 🙂