@Al14
you shouldn't cancel by yourself ever bc if you do then you are penalized with 50-100$ fee, blocked calender, automated review and you are not eligible for superhost status for a year.
If you have instant booking set on then you can cancel penalty free if you feel uncomfortable with a guest or in case of some other circumstances but again, you have to contact Airbnb and ask them to cancel, don't do it by yourself.
also, be careful in case your guest wants to cancel and you get automated message if you agree. You have to disagree bc if you agree then his reservation will be canceled on your behalf like as you canceled it.
When we started hosting we also forget to set higher prices for New year eve and get instant booked. We didn't canceled, they stayed and we lost money ... oh well... now we are smarter 🙂
There is nothing you can do now to reopen your calendar, you can only make another listing