Tuning a harmonica reed isn't complicated, but you should be careful because in the event that you move the reed, it could happen that it doesn't vibrate well in its slot. You will need to file the reed on the tip part (far from the rivet) if you need to raise the note pitch, or on the start part (where the rivet is) to lower the pitch. A little action will be required; often check the way the reed sounds while tuning it.