@Angela2632 sorry but it seems you don't know what are you talking about, you mixed up three options. Go back to your notifications and look if you got 1, 2 or 3.
1) Instant booking - guest book automatically. You just get a notification "Guest X has booked your place from XX to XX 2021. Your calendar is blocked for these dates.
2) Booking inquiry - guest asks you a question. Your calendar is still open for these dates. You answer. You can pre-approve or decline but you don't have to, enough is to answer the question/message the guest. He will later book or not.
3) Booking request - guest requests to book. Your calendar is blocked for these dates. Airbnb is sending you reminders and you have to accept or decline within 24 hours. If you accept the booking is immediately done and you get a notification "Guest X has booked your place from XX to XX 2021.
If your guest already booked and you can't host him then you have to cancel the reservation and will face penalties for cancellations.
If your guest didn't book yet and your calendar is still open for these dates then you just have to tell him not to book bc you can't host him.
Make sure you block your calendar for the period needed to fix the plumbing.