You can add bi-weekly appointments by using the recurring appointment feature in the schedule window. In the scheduling window enable recurring appointments, select Weekly, and change the "Repeat every __ week next days:" input to 2 instead of 1. This will allow the appointment series to repeat every two weeks.
Here's an article that walks you through how to create a reoccurring appointment:
https://help.theranest.com/appointments-and-calendar/how-to-create-a-recurring-appointment
