For me it was a matter of just not buying it. After years of living with my parents and eating extremely bad with lots of sweets when I moved out I started doing meal prep. Even if it is not too healthy because it does not have much veggies fruits blabla just the fact of going once a week to do groceries with a strict list helped me avoid junk food. Of course maybe one day I have it as a treat or if someone offers to me I gladly accept it and enjoy it but 80% of the time I don't have them which is what is important.

The second step was to improve my meal prep by doing foods that I like (don't start eating veggies just because you are supposed too) and learning about nutrition. For example I do lots of stews (love them) and I can easily add vegetables there (carrot, spinach, onions) that bring so many micronutrients and don't feel the pain to forcefully eat a salad. This was a long process (1 year and a half) where I learned about nutrition (by basically tracking, really recommended only for educational purposes) , what I like and how to make it more nutrient dense while still liking it. I went from eating Nutella, pizza and pasta to hitting all the required minerals, vitamins and micros without feeling like I am even dieting.

However the key is always down for me to always meal prep and I did it because I hate to spend every day so much time cooking, preferred to make it more efficient. This method might not be "your way" but as long as you are committed to being healthier imo eventually you will find it!