If your client needs to reschedule their booked session you can follow these steps to do that.
From the main menu click on Studio & Clients » Booking > Sessions.
Locate your session and click on it to see the details.
Click on the Booked session for this client.
Click on Move Booking.
Choose a new Date & Time from the drop down box.
Click Save.
Note: Clicking the 'Save' button will move the session and email your client a new copy of their Session Booked email.