To control a Smart Home device via the Voice Assistant, the desired skill must be activated. Instructions can be found here. In addition, the microphone on the side of the Swisscom Box must be switched on, more on this here.
Then always say "Hey Swisscom..." followed by the specific device or scene you want to control/activate. For example, to turn on a lamp called "Cloud", say, "Hey Swisscom, turn on device Cloud".
More examples would be:
Hey Swisscom, turn on my Sonos.
Hey Swisscom, turn off the light.
Hey Swisscom, turn on the Switch in the living room.