To retrieve an Archived Patient, go to the File menu and choose Retrieve Archived Patient.
A new window will open, displaying all patients that have been archived. Use the Search field to locate the Patient quickly. Once the patient has been located, check the box next to the name and click the Retrieve button.
This will add the Patient back into the Patient ability's sidebar.
To retrieve a deleted patient, follow the same procedure, but hold the Option key on the keyboard while selecting Retrieve Archived Patient from the File menu.