To not know what to do about driving test booking?

[SpiderinaWingMirror]

Driving test booked for 10th June for DD2. For many reasons she cannot do this date ( she had a c section in last couple of weeks).
I need to rebook it but if I try to rebook it just says none available at any point.
Should I cancel the existing booking and give it another try? Does having an existing booking give any benefit or is the system just not that clever? All help or advice gratefully received!

Are you checking far enough ahead date wise? In my area there is a 4 month wait for a test so if you cancelled early June the next available slot would be early October.

I am searching for earliest date and it shows no bookings are available.