How to change your team name Counter Strike Global Offensive
Solution 1:
The command is correct, but it has to be done on the server you're playing on (or remotely using RCON). Also the team names and other settings of this kind are only visible to spectators.
If you're using those commands on your computer they would only work if you hosted the game locally. Joining a server and using them locally does nothing.
Solution 2:
It's mp_teamname_1 "team" and mp_teamname_2 "team"