There are two ways to add a Supremo client to USilio.

From the USilio interface you can click the + button and specify the Supremo access credentials:

USilio - Add Supremo client

The client has been added. You can now manage the Properties or delete the client by clicking the Settings icon:

USilio - Manage client

You can also add or remove Supremo clients from a Supremo addressbook synced with USilio:

USilio - Add client from Supremo