fiddle around

verb2

1. •
   To toy or play (with something) in an idle, fidgety, aimless or unstructured way; to mess around (with); to muck around (with).

   • Stop fiddling around with those matches before you set the place on fire.
2. •
   To tinker (with): to make small adjustments or improvements (to something), especially in an experimental or unskilled manner.

   • I've been fiddling around all morning, trying to get this old lawnmower to work.