The function you use to enable a single note to play a chord is the midi BIND function. To enable binding you simply click on the Bind switch to the right of the section. This can be done on the MAIN page
I am not sure I really understand what the issue is, I thought it was about key binding. Can you please export the Scaler state where you are having the issue and upload it here. Then it may be possible to recrate the issue and try to explain what is happening.
Can you also clarify which option of Keys Lock you have chosen when this happens:
In the settings you can change the binding of the chords to a lower octave. You can then play the notes in the higher octaves to write melodies without accidentally triggering the chords. I’m guessing that’s the issue?