Let you choose your instrument when opening the app
Instead of having to go to settings each time you want to change instruments, let a user who is learning multiple instruments pick the instrument he wants to play when opening the app.
OR at the account creation, indicate the how-to switch (when I tried to switch to another instrument I did not thought is was possible)
Paul Green commented
I really like the sound of this - or have a way to quick-switch the instruments maybe - I get when learning it's no big deal, but when I just want to jam and play a few songs, I might want to alternate between bass and guitar.