There’s a harmonica guy who tunes melodicas at this site:
The two photos on the bottom right show him tuning a Pro-37. He has a microphone attached to a tuner, a shim, and some kind of electronic (?) device he’s using on the reed. Is the device an engraver? We can see that he’s pinging the reed with his shim. There are burr bits of varying sizes available for pen style micro engravers.