If the pre-approval expired, you should be asked if you want to pre-approve again. If too much time has gone by, you can just message the person to re-request, and then you can re-approve!
I supose your time to respond on booking request expired? You have just 24 hours to respond on reservation request, if you don't then you are penalized by blocking those days on your calendar. You should install Airbnb application on your phone so it doesn't happen to you again.
You can try to contact Airbnb and ask them to unblok those days, say you are new, didn't understand the system etc... and you will see.