It means that he will try to help Siwon :c
His hero personality he wishes he could have helped the original Si Won before he had committed suicide like he had saved Min woo Jin when he was a child. So hes going to meddle in these affairs and get revenge on them for being terrible people
Right he's a bit aloof in that he minds his own business. He's not interested in getting back at people who bullied Siwoon. Right now, all he cares about is experiencing high school for the first time, never mind the fact that he's running away from the issue of his original body. He only acts when others try try to provoke him.
What does taemin mean by meddling and why does it show a picture of him when he was a kid when he first meet woojin.