You will need to build up habits, slowly. Discipline is mostly a collection of habits. Look at Atomic Habits for example. If you can't manage to read the book (or listen to it), there are some YouTube and TikTok videos about it. Or a first habit to implement could be to read the book for 10 minutes each day before going to bed (tie it to something you do every day).
Another angle might be mindfulness training (meditation). If you can become more aware "in the moment" of when you become distracted or side-tracked, then it should become easier to preempt it.
Another angle might be mindfulness training (meditation). If you can become more aware "in the moment" of when you become distracted or side-tracked, then it should become easier to preempt it.