Definition of fiddle:
(n) :
the
violin when played in any of various traditional styles, as opposed to classical violin; an adjustment intended to cover up a basic flaw
"when I play it like this, it's a fiddle; when I play it like that, it's a violin."
(v) :
to play aimlessly; to adjust in order to cover a basic flaw or fraud etc
"I needed to fiddle the lighting parameters to get the image to look right."