If you didn’t do so when originally scheduled, you can add a Virtual Meeting Link to already-scheduled Appointments.  Just click to modify an Appointment and, so long as it’s of a type that is set to 'Always' or 'Usually' have a Virtual Meeting, you’ll find a button by which to do so:

When modifying an already-scheduled appointment, you can see the corresponding Meeting that has been scheduled:

Note the “Location” field has been set to the exact URL by which you and your clients will be able to access the Meeting.