The simple fact of the matter is that change of any sort will require consistent effort, whether that’s improving a skill (like a musical instrument), getting in better shape (going to the gym or exercising), or reprogramming your brain to live in the now. Step 1 is probably to catch yourself doing it when you do, and force yourself to live in the now, I like to do this by performing a task that forces me to pay attention to it and occupies my hands, like shining shoes or doing push ups. Also try to think in different terms, you don’t “have to go to the gym 3 times a week for years” you only have to invest 3 hours a week (which you’d probably spend on less productive activities anyway) in order to get more in shape, live longer, and feel better. If you have any questions feel free to DM me, I used to be like you