What is the first step???

My Doctor is supporting me to have the Gastric Byp Surgery done here in MI. I have Hypertension, Diabetes type 2, High Cholesterol, High blood pressure, It has been deemed neccessary, very. I wanted to know who sends off the letter, and who do we send it to? Do we get permission first from the insurance company , is that who we are sending the letter to? My doctor sayshe will support it in any way he can.... Does this sound like I have a pretty good chance for help???