Sure for me these worked.
-I found a "safe spot". My bed is my safe spot. I don't leave it until bad thoughts leave except for the bathroom and I don't allow myself to do anything except use the toilet and wash my hands then I go back to the bed.
-While I'm sitting or laying on my safe spot I try to identify why I'm feeling like this. Then see if I can change the circumstance, or better yet my own viewpoint on things.
-I found somebody I can talk to that is understanding. Note I said "understanding" not "approving". A mature adult is best situated NOT a peer who thinks whatever makes you happy is good. Mature ones who have dealt with similar feelings in the past and are in a good place now are the best for talking to.
-I stopped hiding the scars. The shame factor is very healing personally. If I'm going to do something why hide it? Until you're ready to deal with the consequences of your actions you're not going to be motivated to stop.
-I got help for the underlining issues. Depression, anxiety, numbness, etc. pretty much all have causes whether it's chemical or environmental you have to be responsible for your own emotions. NOBODY CAN MAKE YOU THIS WAY you allow yourself to be this way. Fight negative emotions with positive logic. It won't always make sense and it won't always connect but trust that if you change your perspective on life to a more positive outlook you can live with the worse of things.
-Build a strong faith. I'm not just talking about religion but that can be helpful in its own way. Have faith that you are going to make it through another hour, another day, another week. However long as you can go be proud of that time and say next time I'll double that. I've gone over a year I can make it to two.
-Some say they hurt themselves to punish themselves, that's an environmental thought by the way.

I had that thought too. Here's a new thought. Denying yourself the right to SI is just as strong a punishment as giving in. You'll be more miserable at first cause you DO go through withdrawals. Or at least, I did.
-I stopped saying "can't". I CAN quit. I CAN walk past any tool I've used before without picking it up. I CAN find positive things in my life. I CAN keep hanging in there. I CAN be strong. Later those are replaced with WILL.
It's not easy to change your entire thinking. But you CAN do it one step at a time. Also using the sticky of other things you can do instead are very helpful. I still draw on my arms and legs with marker but now they're signs of love and not hate.
Remember you as an adult can now choose your life and there's tons of people who are wanting to protect you. You just have to reach out and find them.