muck about
verb
Definitions
To do random unplanned work or spend time idly
Example: Stop mucking about and get on with your work!
To attempt to do something with a piece of equipment without understanding how it works.
Example: Don't muck about with the video machine, or you might break it.
To be playful; full of fun and high spirits; to not treat the situation seriously.
Example: It was only a joke. We were only mucking about.