If you need to add any extras, or edit anything on a booking that has already been checked out, you will need to rollback the booking.
Rolling back a booking will revert the booking status to 'Checked in'
To do this, select the booking you need to rollback and click view booking.
Once on the bookings page, you will see a button in the top right-hand corner that says Rollback booking.
Click Rollback booking, enter the reason for the rollback, and finalise.
If you are integrated with Xero, you will need to void the previous invoice in Xero to avoid double-ups when the booking is checked-out again. For more information, please see this help article: Rolling back a booking & voiding the invoice