Tell them that under no conditions will you ever fly with them on a 737 MAX, an abortion of an airplane, unfit for first-world people, and for which Boeing tried to hack a fix with control software.
American Airlines:
https://www.aa.com/contact/forms?topic=#/
Southwest:
https://www.southwest.com/contact-us/contact-us.html
Alaska Air:
https://www.alaskaair.com/content/about-us/contact-us/phone-numbers?lid=nav:contactUs#customer-care
United:
https://www.united.com/en/us/customercare
Delta:
https://www.delta.com/contactus/commentComplaint
JetBlue:
https://www.jetblue.com/contact-us/
Be polite but firm about your opinion on this dangerous aircraft. The 737 MAX program must be cancelled, and Boeing can suffer the consequences of its actions.