To have your drivers return to start at the end of their route, open the "Drivers" tab.
Click the pencil icon on the driver profile you want to edit. Set the "Start Address" and "End Address" to the same location. If you leave "End Address" empty, Routific will assume that the driver can end their route anywhere, and the route will not be optimized as a round trip route.
Click "Save" to save your changes.