I don't know your particular model, but I had trouble with my Hohner Chromonica when a reed stopped sounding. I removed the cover plate, which is secured to the body by two screws, and using a wooden toothpick, I carefully removed some debris that had got into the gap in the reed. I then screwed it back together again and it worked fine. Another thing I regularly do is to remove gunk that builds up round the holes. A wooden cocktail stick does fine for that job.

I must admit I have always been wary of washing my harmonica as it is wooden bodied, but I suspect that a fairly quick wash in warm soapy water will do no harm, but be carful round the reeds. In fact I believe some of the old blues players used to soak their Marine bands in water before playing as they said it made them play better. I think that the soaking made the wooden body swell and sealed the reed plate properly so there was less air leakage.