Getting an already enabled device into a home group with Alexa

Just having probs putting a device which is already connected to my Alexa dot into a home group :joy: which is a TV connected via vsmart, works with Alexa.
Also wondered if anyone knows how to then command Alexa dot to be used for cinema sound, if not then finding the TV which is already connected, is it because it is not in a room.
Thanks if anyone knows :relaxed: