What are good ways to help someone quit smoking?

My friend’s fiance has a sever breathing problem stemming from smoking to much a day. He’s 28 and on oxygen tanks. His doctor says he’s sacrificing his life. My friend can’t get him to stop because he refuses and were’re all worried. What are some good quit tips. Also what are some effective ways to comminicate with him to stop. Thanks a lot!
My friend lives we his fiance. They are living a very tight budget. They get their money from ss.