You will never lack willpower again
Exercise hold your breath for 15 seconds - Holding your breath obviously, that's a little a bit of a willpower challenge. This ability to hold your breath is one of the best predictors of people's ability to succeed at difficult goals this is called distress tolerance ( the ability to stay put when things get uncomfortable).
There are 2 challenges on how basically ride out physical discomfort that gets in the way of making a difficult change.
Surfing the urge - learn to pay attention to the physical discomfort of wanting something, you give it your full attention and you trust that you can tolerate those physical sensations, and if just you wait with patients, they will go away. Any craving, any emotion will eventually pass if you can just breathe and wait it out, you don't have to act on every act of impulsion. Can give us a lot of willpower for the things that we need willpower.
Mindfulness to allow yourself to feel what you're feeling or think what you're thinking. Attend to the experience rather than immediately try to escape it.
Use the breath as a source of stability, you know what you're feeling, take a few breaths and broaden your attention out, and look for the first opportunity to recommit to your goal.
Train your willpower physiology - meditating, sleeping, exercising, and eating a diet.