Before moving or updating the date & time of the bookings, you need to make sure that you have created a new available event of the time and/or date you are moving the bookings.
***click here for the steps on how to add a new fixed time schedule: http://help.flexbooker.com/en/articles/5614058-creating-a-new-event
***click here for the steps on how to add a new event:
Under the "calendar page" select on the session or time slot to edit:
Underneath the "current bookings" label there is a right arrow button:
This action should allow you to move all attendees within the session
Select on the new event (date and time) on the calendar > you should have a confirmation to move the bookings, this is to ensure and allow you to review on the change/s you are about to make:
Select on "Yes, Move Now" to update the date and/or time of the event.