You have to practice to improve
Have you heard things like "Just do it," "Start small," and "Divide into smaller tasks"? Yet, sometimes you still don't find a way to get things done? I'd like to add an extra thing that I've noticed helps me: practice.
When you learn math, you're given an example, you understand the concept, but only after doing some exercises do you truly grasp it. The more problems you solve, the better you become.
Similarly, when learning new dance steps, the instructor (or video) demonstrates the moves, but it's only when you try them yourself that you start to get it.
The same is true for discipline, but unlike math or dance, it's not as easy to measure how good or bad you might be. For instance, no matter how many times you try to "just do it" to solve an advanced calculus problem, or how many times you try "it's just a five minutes task" to learn a professional choreography, it won't work if you’re not an advanced dancer.
Likewise, you can't just go to the gym or finish a project if you haven't mastered smaller habits. So, find a small, uncomfortable task to practice on. I use "washing the dishes" as an example all the time because I was terrible at it. Once that becomes easy, you can move on to something else and continue building your discipline muscle.
For the past year or more, I've been trying to write in my free time as a hobby, and often I procrastinate because it feels overwhelming. However, during this time, I've improved in many smaller tasks (like flossing my teeth or drinking water). Today, when I tried to write again, it was still difficult and overwhelming, but I managed to make some progress. Before, I would have just resorted to playing video games. I realized that my improved discipline in other areas helped me achieve this. These small wins remind me of the satisfaction of completing a task and create a positive cycle.
So, assess what you're trying to improve. Do you need to take a step back, or even two? Practice those smaller steps, master them, and then gradually incorporate more.
I hope this helps.