How to help but not get too involved?

So I got this friend that I used to work with who’s basically being bullied by 3 guys at the job.
They did the same thing to me but I was too scared to do anything since they knew my address so I didn’t want them to come over but I know they’re all talk about that but didn’t want to risk anything. The guys got 1 warning out of 2 to get fired. The guy told a manager and the manager told HR and they said it’s he say she say even though he had evidence it happened. Yesterday I was talking to him and said I’ll go to the store to talk to the store director because he’s the top guy. I told my parents and they said don’t do it I’d just be dragging myself back into the whole situation that I left the job to get out of. I’ve told the friend to quit, change locations (since there’s 3 within a 10 mile distance from each other), come to my job. He keeps saying “idk this place is so much closer”
How to help but not get too involved?
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