If I'm afraid of an injection, then I just inhale and detach from myself and my body for a couple of seconds when the injection occurs, I look at the finger or vein as if it were not mine.
I did this, I asked the nurse and the one who gave me the injection to inject it unexpectedly, so I did not feel pain at all, but only a short bite from a mosquito.
Don't look. If an injection is given to you, then look the other way and think about the good. Imagine yourself where you want to be.
If you do the injection ... then inhale, exhale and go. The more practice, the less fear, you just have to do it.
A very simple but really working method helps. Take a deep breath and exhale. Think it won't work? Try it and see the opposite