And now I have one leg four inches longer than the other from all the pullin'?

A jew's harp as generally used is not a "tuned" instrument. When a "weakly resonant" sytem (the harp) is coupled to a more strongly resonant system with higher pitch (your mouth), the more resonant system will "pull" the lower pitched and relatively "unresonant" system to the stronger higher frequency.

So to tune a jew's harp "up" you put a marble in your mouth.

If yours has gone flat, it's 'cause your head's swelled up. Shut yo' mouth a bit, or put your teeth back in.

Seriously, it is "convenient" to have the harp "reed" floppy at a frequence close to, but a little lower than the "mouth frequency" that's comfortable for you to play at; but "tuning" in any real sense is not a commonly used term for this instrument.

John