I learned over years of growing up to be the calm person in any relationship.
My mother was calm, patient and meditative. Being an artist, she was always contemplating her work. I gradually became more objective, less judgmental, more open to conciliatory communication with those I found offensive. I became a teacher and put those traits into teaching my students.

I like your approach to conflict. My exes couldn’t grasp that

Dealing with conflict isn’t my string suit either. I wouldn’t say it’s a bad habit though, I do the best I can; like most people, and learn from others that have put forward theories of improvement. My father had a violent temper, my mother was super passive. I have vowed to be neither, with varying degrees of success!

Understand that it's about learning and practice. As you do this you'll make mistakes. Learn from the mistakes and how to avoid that mistake again. It's not about willpower: there is no such thing as willpower. Just continue to practice and you'll get there

I quit both smoking and drinking 28 years ago. There's more to it than I can give here, but changing a bad habit includes these:

1. There's no shortcut. You have to do it.
2. Visualize yourself as a person who doesn't have that habit any more.
3. Recognize your achievement every day and give yourself some private celebration.
4. Don't advertise what you're changing. You don't need pressure from others or fear of public failure.

Calm is how I survived an abusive relationship. He tried to kill, me and after I got away, I calmly left and worked a plan but before that calm was the only way to diffuse him when he became volatile. I'm still here, so I won. To break a bad habit, I've used tapping. It seems weird but it actually works.

[thetappingsolution.com]

I don't understand the wording in this piece at all but I will reply according to the title "How Did You Change a Bad Habit."

As a young teen my cousins and I experimented with smoking. Not unusual. Later in the Army, others there showed me how a cigarette and a beer went together. I then started smoking only when I drank once a week. Getting back into religious roots later, I decided to stop smoking 2 or maybe 3 times "for god." That did not work. You have to stop a bad habit for yourself. Then I learned that if you stop smoking a few days and start again you get higher than a kite for 10 minutes. Oh, boy. Next, I got the flu and could not smoke. Once recovered I started smoking again. About 20 years ago I got the flu a second time and could not smoke. This time around I was smart enough not to pick the cigarettes back up.

That's my flawed story of changing a bad habit (actually dropping the habit) through my whole life with it as a thing that controlled me off and on. I do not want cigarettes today and I do not miss them.