Undo check-in or check-out
From the reservation
Go to the reservation form whose check-in or check-out you want to undo. Click the icon next to the check-in or check-out time. This will undo the check-in or check-out.
From the planboard
Click the reservation in the planboard whose check-in or check-out you want to undo. The reservation overview appears on the right side of the screen. Click 'Undo' at the bottom.