@Jerry116 I notice you cancelled a confirmed reservation. Host cancellations will automatically block the dates of the reservation in your calendar. There is no way for you to unblock them. It is one of the penalties applied to hosts that cancel confirmed reservations.
If you had a good reason to cancel the reservation that fits within AirBnB "penalty-free" cancellation guidelines, you can contact AirBnB support and explain what happened. If AirBnB agrees that you should be able to do that cancellation penalty-free, then they will unblock the dates and remove any penalties.
In the future, please do contact AirBnB if you need to do a host cancellation before you do the cancellation!