Building new habits or replacing old ones has to start small, so small actually that the book I read about this a few years ago is titled Atomic Habits. What it breaks down to is that changes in our daily lives don't happen instantaneously; they take time, effort, and repetition.

For example, if you were to set a goal of getting more fit you wouldn't accomplish that in one day. What you can accomplish though, is to go out and walk a mile today. Then the next day walk another mile. And the next another mile. After a week or two of this, you might try something more intense like longer distances, jogging, or maybe even riding a bicycle. But you didn't get there in one day: you worked at it a little bit each day until it naturally became part of your habits.