To edit existing appointment slots, navigate to your calendar and click on an appointment slot to edit them.
Once you've clicked on the appointment slot to edit, update the desired changes and click "Update." Note that clicking "Cancel" will not change any details of the appointment slots, while clicking "Delete" will delete the appointment slots.
Note: when editing an appointment slot, the option to have the appointment slot repeat is no longer available. As such, to have the appointment slot repeat, you will have to create new appointment slots and choose repeat options at that time.