1
to finger;to touch;to play with;to fiddle with;to toy with
その鍵をいじるな!
Don't play with that key!
2
to make changes to;to tinker with;to fiddle with;to tamper with
書類は勝手にいじられた形跡があった。
The documents were tampered with.
3
to dabble in;to do as a hobby;to play around with
子供がおもちゃをカチャカチャいじっている。
The kid is clanging away with his toy.
4
to tease;to make fun of
also as イジる