I’ve been having this issue with the home app and Google assistant for a while but recently found a fix so I thought I’d post it.
the issue was: saying “hey Google, [command] the office lights” would result in Google assistant responding that the “device hasn’t been set up yet” and that I could do so in my Google assistant settings. Asking Google to control other rooms would result in the incorrect lights being controlled that would not match the current room/group setup in the home app. No amount of changing/deleting rooms in the Google home app fixed the problem.
To fix this I had to go into my routines, edit a routine, add “adjust home devices” command, adjust lights plugs and more, then select “home control settings”. Under the rooms tab I could now see the incorrect room setup and adjust it there. I had to completely rename the offending room (living room) before I could delete it. Then I remade it and added the correct lights.