Hohner Melodica is a 50s-era keyboard instrument which sounds close to a harmonica and which you play with your mouth. Cool-looking, but the one I got from someone to review has a non-working G#. It's like the note is blocked for some reason, because I can't blow into the unit when I only press that key. It's a very inexpensive instrument and I don't think it can be opened up. Is there a fix, or is it hopeless?
You can open up a melodica. There are screws holding the back on. Once you're inside the cure may be obvious.
But they're still for sale, and cheap. So don't waste too much time on it.
Open up the Melodica. There should be screws on the back. Once inside you will be able to see the reeds and any obstructions if there are any.
This video is for one of the Yamaha melodicass, so the internals may be different, but it should give you an idea of what you should expect to find inside -