Ok its not easy to advise you fully as I dont know you what the specific issues regards to health are or the history of the problem but I will do my best to be quite general.
Are you a good visualiser? If yes great! Good place to start, if not its something you will need to work on. I would recomend working through some of Josephine McCarthy's work.....you will find her first module here
https://www.quareia.com/apprentice-module-1 all freely available online.
Once you have got visualisation down then its about practicing going to different places, events in your life. I find smell very good for this, i imagine smells that remind me of something, for example rolling tobacco and soup remind me of my great gran and granpa who I lived with when young so I can imagine those smells which takes me back to a particular time in my life.
Now tackling the underlying issue, changing to healthy habbits throughout your life is going to be very difficult. The best way I feel to deal with this would be to go back to the root of the problem, if its overreating, drug taking etc then you will want to discover why you have been punishing yourself and fix the issues from there. I could recomend many ways to help you discover underlying issues but again its hard to do as I dont know the details. If you want to discuss it privately feel free to PM me.
All in all this is going to be a long and difficult task but the results would be great. I wish you luck on your journey.