How do I stop myself thinking to self harm?

I think you can start by doing something else, like your hobbies, that will distract your thoughts from doing self harm. It might help you as your mind will be focused on the things you're doing at the moment. Another option is to talk about it with your closest person like you family, friends, or you can also talk it here with the listeners. Talking about your problem will make you think about the consequences clearly and stop you from doing something that you will regret in the future. Your parents and friends might also give you some advice that will help you in the future