FIFA 12 on Wii has no built-in "reset city" option. The only ways to start fresh are destructive:
EA omitted city-reset in FIFA 11–13 due to database complexity. Later entries (FIFA 14+) on newer engines added "Restart Career" but Wii versions were legacy ports without the feature.
If you just want a new manager profile, create a new Mii and select it when starting Career—some data separates per profile.