So it's an octave harp then. Tune the top row with your tuner (or to your satisfaction) then tune the bottom row by ear to tune out the beats. It's a devil of a job as the tuning will change when you put the covers back on (it's an embouchure thing). There should be no tremolo effect with an octave harp, but that's a counsel of perfection. Try to identify the exact reeds that aren't sounding. Ping them a few times to free them up and make sure they're gapped the same as the partner reeds, otherwise they won't work properly. Check that they are free to move in their slots. Good luck with that. You'll need it!