You are starting with a single-note melody and a chord track.
Duplicate the track with the melody. Or copy the part to another track
Set it to follow Chord track - try the “chords” setting
See how that works - you may have to transpose the notes higher or lower to get in the vicinity of where they need to be.
I don’t work this way personally, but I just tried it and it works well.
Check out this thread for more ideas - there seem to be several ways to get there
If you are with an audio track, there is a feature that generates harmony parts - explained in this video
