Sometimes it's useful to be able to add records of Appointments that have already happened with your clients, such as to have a complete record for logging your coaching hours or capturing what already happened in an Engagement.
You can do this by scheduling a new Appointment in the usual way.
Simply use the date picker to choose whatever date you like in the past.
You can even schedule a series of appointments in this way to quickly log your hours, if your past appointments were so regular. :)