As they say, motivation follows action. I'm not particularly motivated to do it, I just tell my hand to shut off the hot water and then I deal with the consequence.
I'm sorry you feel that way. I started with cold showers because others have said that they boost discipline. As James Clear says in Atomic Habits, "Every action you take is a vote for the type of person you wish to become." By flipping the water to cold, I'm telling myself that I'm strong and disciplined, even though I feel so far from it.