Cleaning is not always a good thing. If you don’t know what you’re doing, you could damage the harmonica. Clean the cover plates if they are dirty. This is perfectly safe. But cleaning the reeds requires a little care. It’s easy to damage them.
You can open the coverplates of your harmonica to see the reedplates. If they look shiny and clean, put the covers back on. There’s no need to clean it. But if they look dirty, you should probably clean them. Dirty reeds make a harmonica sound out of tune.
There are lots of videos on cleaning harmonicas on YouTube. Just try searching “cleaning harmonicas”.
Cleaning the Harmonica
How to Clean a Harmonica (Mongoose free method!)