My harmonica went out of tune, what should I do? Do i need to dissemble it for tuning?
There are videos online which detail this, but the key is, the longer the reed, the deeper the note. Problem is, of course, that it is easy to sharpen a note and hard to make it flatter.
And yes, you have to open up the harp to get to the reeds, but that is just two screws. Or, entry level harmonica are like $5 and my Marine Band was $20, so they are very replaceable.
I go to Adam Gussow (KudzuRunner on YouTube) for all my harmonica questions, including how to tune them.
Harmonicas should be in tune when you buy them, and should stay in tune for a long time. Tuning them is not something you should expect to do often.
However, it is possible. You need to open it up to expose the reeds. You can remove metal from a reed using a filing tool, and you can add small amounts of solder to the end of a reed.
To sharpen a note, remove some metal from the tip of the reed, making it vibrate faster.
To flatten a note, remove some metal from the base of the reed, making it vibrate slower (because the weight at the end is higher relative to the base)
Or, to flatten a note, add solder near the tip.
Use lead-free solder; this thing is going in your mouth.
More details, and my source, at this web page.
If a harmonica suddenly goes out of tune it's probably due to a reed that has gone bad (e.g. cracked). You may be able to tune it up, but it will likely go out of tune again very quickly. It is possible to replace a reed, but probably not worth the effort.