Taigini

Hey everyone, I recently bought a new LG SmartTV (43UN71) and I see it is connected to a laptop of my roommate (who doesn't own the TV). It is connected as a media server and this is really bothering me, because they have streamed Youtube once to my TV (by accident), but I do not remember ever granting permission for their laptop to connect to my TV. How do I remove their laptop as a media server from my TV? Thanks in advance!