Instant booking

[Mariana17]

I active my instant booking but actually I didn't know how it's working.
I'm dealing (not confirm yet) with one guest for staying 3 months and this morning and I check my reservation three two instant booking finalised.
I know that really bad for the guest I already deactivated instant book.
But how can I proceed to cancel this bookings?? Preference without penalties and no blocked dates.
I'm feel very disappointed with me but I'm totally inexperience.
Thanks Mariana