Select Appointments > Configuration… > Appointments Statuses
Place a check in the "Include inactive statuses" box to include inactive statuses in your search results.
Use the Show All button to view all appointment statuses. Or use the Search field to further drill down your search.
Select the appointment status.
Click OK when the “This appointment status is currently inactive.” pop-up displays.
Uncheck the Make this status inactive checkbox.
Click Save.