To add a new template on to an existing department, navigate to Administration>Departments. From there, click on the desired department.
Once the desired department has been selected, navigate to the Templates section and input a name and display name in the respective fields (it is recommended to have the template name and display name be the same). After doing so, click Add New and the new template will be added to the list on the left
Repeat the above process if you need to add more than one additional template. Once you have added all additional templates, click Save Changes and the templates will be saved.