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

When modifying an already-scheduled appointment, you can see the corresponding Zoom 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.