You can change workers who have been allocated to a booking using the deallocation button.
Select the workers you would like to deallocate from shifts using the tick boxes or use the all link to select everyone
Click the 'Batch Edit Shifts' button
All shifts highlighted in green will be amended, deselect any shifts that don't apply by clicking within the box
Select deallocate- the number of shifts being affected will be shown in brackets
If shifts have been 'published' then you'll need to select a reason for the worker being removed from the booking