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.
The trick is back-dating them.
For good reason, the calendar date picker doesn't allow you click on a date that has already passed (this is a handy, mistake-preventing measure that is welcome 95+ percent of the time!).
BUT you're still able to manually enter whatever date in the past you like, simply by clicking on the date input itself and typing it in.
Note: on smaller screens (like a smartphone), the date picker pop up widget might be covering the date input. In that case, scrolling up or down a little will often do the trick.