There are two things I do in order to overcome SI that've been working for me. I can't assure you if they will work for you because everyone is different, but maybe you can try this:
1. Make peace with the concept of death and whatever comes after you die. It has been pretty useful for me to not feel afraid of what comes after. I don't have specifics believes on the matter, so I just visualized any possible outcome (reincarnation, hell, astral experience, etc) and made peace with each of them. I think that SI has a link with the fact of us being afraid of an afterlife, so if youfind a way to not be afraid of it, you are closer to overcome SI.
2. Methods: you'll find that some methods are more convenient to you than others, due to your personal determination in choosing what better suits you. Desensitization of the method will help you became more confident about how it will work for you and makes it more factible for success. What I mean through this point is that one should expose oneself to the method multiple times or become more aware of it in order to not feel scared. It helps to diminish the emotional responsiveness.
For example, at the moment I'm planning to attempt full hanging, so I get used to the feeling of the rope in my neck, practice with partial to experiment the pressure I will feel, watch videos of people hanging themselves to know what to expect of the feeling and my body hanging, etc. Just for you to accustom to the fact that you are going to die.