Fiddling is an informal word which has more than one meaning.
The teacher was annoyed by his constant fiddling with his mobile phone while she was trying to explain ...
(meaning - playing with, touching and moving)
The chief accountant was arrested for fiddling the books.
(meaning - criminally falsifying the figures in the accounts ledgers for someone's gain)
In the past it was also used to mean playing the violin (fiddle) although this use is not common now.
Student or Learner