does anyone can teach me how to quit from other team?

The fact is I played online with my friend, and I take control the both teams as I am curious about his team tactics

However, I cannot find the way to quit from his position as he cannot take his team back?

Is there anyone can tell me the way to quit?

Only quitting and reloading (after saving, obviously). You cannot quit a game or a team without quitting a game. Thus staying in the game with one team while quitting as the other wo't work.

When you play network games make sure that you are using passwords as otherwise the host will automatically be in charge of all teams without a password and, as said above, you wouldn't be able to change that. So if that is the case you will have to retire your mate's manager and he will have to create a new one with a password.