If you mean adding notes that don’t belong to the diatonic scale (i.e. a “chromatic tone”, which doesn’t belong to the chosen scale), you can use “.” and “,” to raise and lower a semitone any selected melody note.
If you mean adding notes that don’t belong to the diatonic scale (i.e. a “chromatic tone”, which doesn’t belong to the chosen scale), you can use “.” and “,” to raise and lower a semitone any selected melody note.