Minor chords can print as a dash (C-) or a lowercase m (Cm). Turn Use m for minor on or off to choose.

 

It is in Chord Chart Settings (the Aa button on iPhone, iPad, and Mac, or A on Android), and in Settings on Windows. The setting only changes what you see; the chord is stored the same way whichever you pick.

 

For more, see Change how your chord chart looks on the iReal Pro website.