Like I've said, life is an illusion. There is no past. There is no future. There is only the present moment. Everything is a moment. The past is just thought memories of a present moment. Life's experiences are merely thoughts of our so-called reality experiences. In order to change certain past moments, you need to connect with a moment you experienced in your so-called past reality.
You could communicate with your past self simply by focusing on a "past moment". Since, all your life's experiences are only experienced in your mind, you are just simply tapping into a "past thought" and focusing on a change. You can give yourself advice or give yourself necessary information. I've been doing this for over a couple of years. I realized as I look back into my childhood, I knew things that I shouldn't have known. I knew things that only people with experience would have known. There is a change. This works, but you have to focus on a moment that your specifically know that your thoughts can access the subconscious. A relax moment, if you will. You can even do this intentionally for experimental purposes.
One exercise would be to lie down and not think of anything for about fifteen minutes. Don't do anything. Just listen to any intuition. Maybe a feeling or something. Don't try to force it. Just simply relax.
On the next day, go back to that "past moment" and focus on you trying to communicate something to yourself. It's like telepathy. And since "it's you communicating with you", the effort is easy.
You have the power to know the future, by simply living the moment and communicating back to the past self. If you keep doing this, you will experience frequent "deja vu" incidents.
I developed this "mind time travel" a couple of years ago. Go and experience it yourself. It does work. Maybe, you can not change traumatic incidents at the start, but you can start with trivial things. As you experience strange altering moments, you can dive in into more complex situations.