@Maricela19 You can't fix it. That's Airbnb's punishment to hosts for cancelling a reservation. Now you won't be able to book that period at all. And the first review on your lisitng will be "Host cancelled this reservation xx days before check-in", which looks bad to potential guests, because, of course, no one wants to get cancelled on. It's really so important to have all your pricing in place before you go live with your listing. And pretty rude to guests to cancel them because of the host's error.
What you could try is to call Airbnb, tell them you're a new host and didn't understand how any of this worked and maybe they'll give you a pass this time and open the calendar.