Go to the grocery store when you’ve already eaten.
Allow yourself to purchase 1 kind of junk food per week only (it’s ok to have a treat, going whole hog can just make you go back to buying crap). Purchase health snacks as alternatives to the rest. Personally I go for things like cashews, carrots, and healthier chips (I can’t eat anything with gluten, so already forced to avoid some things. Because of the GF health craze that hit some years ago, a lot of GF foods are fairly healthy, so you may want to look at those to make it easier to start selection).
Schedule time to do meal and snack prep. Watch something while you make it, I like to re-watch shows so I don’t have to pay a lot of attention to them while I cook. I work from home, so it’s mostly stuff I can combine with other things - tons of rice, chicken I can add to rice to make fried rice or drop in some soup with rice noodles, etc. You’ll need to figure out what type of foods you want quick access to.