You can restore and reopen any visit checked out within 24 hours very easily!
Check the patient back in (via Instinct or through your main practice software) and then find your patient on the Status Board.
Open their treatment sheet and select ‘Visits’ at the top of the screen. Find the previous visit and click the 3-dot menu as shown below:

Click ‘Reopen’ and this will restore everything as good as new! You have up to 24 hours to ‘Reopen” a previous treatment sheet.