You can make any change to your bookings before the time starts.
If a booking time has started, your Support Pro will need to submit with changes.
Find the booking you want to change in your Upcoming Bookings list.
Click the booking you want to change.
Then click the Change Booking button.
Just make your changes, check the summary again, then click Request Change.
Your Support Pro will be asked to accept the booking changes.
If they don't or haven't accepted the changes, the original booking is still active.
The changed booking will show in Tasks until the Support Pro approves the changes.