Fetching details from the dictionary...

to finger; to touch; to play with; to fiddle with; to toy with
to make changes to; to tinker with; to tamper with
to dabble in; to do as a hobby; to play around with
to tease; to make fun of
to grope; to feel around (in one's pocket, bag, etc.)
彼はペンを弄りながら話していた。
He was talking while fiddling with a pen.
コンピューターの設定を勝手に弄ったら動かなくなった。
It stopped working after I fiddled with the settings.
面接中に髪を弄るのは緊張やストレスの表れだと言われる。
Playing with one's hair is a sign of nervousness.