I have struggled extensively with self harm and suicidal thoughts, more than the average person. It's a delicate situation, as most people(About 95%, just throwing out this number based on my experiences) are too embarrassed/scared to talk about it. The biggest thing with Self harm is that, I bet they don't want to do it, but it legitimately helps a ton. When you say self harm, I assume self mutilation. Now, it's not healthy, so you need to let them know that you understand why they do it, you need to let them know that it's normal, and that they need to find safer alternatives to let out their emotions. You never want to seem forceful or back someone into a wall with this, cause it only makes their emotions become worse. If you take a more upset/forceful approach, it'll only make them feel more broken. It's very difficult tip toeing on ice when someone is hurting themself, but it's what you have to do, tip toe. This is all just all of what I've seen, it's not at all supposed to be a generalization, cause I'm sure there's some cases that don't match up.