Practice choosing discomfort.
Our choice is between doing an uncomfortable thing now or having greater discomfort thrust upon us later. Because we procrastinators suck at choosing the lesser discomfort now, we effectively are choosing greater discomfort at times that are out of our control.
Making that choice is a skill. It has to be practiced to be developed. You can’t just start doing it easily today just like you can’t just start doing anything that requires skill.
A month of cold showers is an excellent way to get practice at choosing discomfort, btw. It’s easy to do. You’re (presumably) going to be taking showers anyway, so it’s just a miniscule modification to your daily activities.
All it takes is a single moment of strength to put yourself into the water. It’s one big rep for your discipline muscle every day.
To get the most out of it, focus on the negative feelings you experience while making the choice to get into the cold shower. Those feelings that are crying for you to avoid the discomfort are the same feelings that keep you from doing your work when you should. Those feelings are your enemy, and to defeat them you must be conscious of them. Feel them, observe them, hold them in place, and eventually you can control them.