Can't delete chords for modulation

I’m having an issue with the modulation. I’ve chosen four nice chords and deleted the rest of them in the ‘c’ section, however, it doesn’t let me modulate these, I need to click on ‘modulate’ in the ‘b’ section which makes me use 7 chords (in this case, which is e minor). I watched a youtube tutorial where the person removed certain chords in the ‘c’ section then hit’s modulate and then gets those 4 seperate chords in the modulation section, however this does not happen for me, any idea why this could be?