Hi @Nita1732
Mistakes happen, but the blocking of the calendar is part of Airbnb's cancellation policies for the reasons @Mike-And-Jane0 mention.
One option which might have been possible was to do a Reservation Alteration instead of cancelling the reservation, but of course we don't know the particulars of the reservation involved? Another option would be have the guest cancel and provide a full refund and then have them rebook other dates. That would have allowed your calendar to be open for other reservations instead of being blocked.