I have friend who has back pain, knee and Breathing problem just for drinking and inactivity. Now he wants my help. What should I do?

Just be inspiring somehow and motivate him. Encourage him to at least slow down on the drinking. He could do stretches for the back pain. Taking hot baths would ease both the knee and back, maybe at night before he goes to bed. I had a similar thing. I had an older guy friend that was an alcoholic and had a bad arm that bothered him. He told me he wanted to start taking walks and start getting healthy. I told him I would take walks with him, but never got around to it. I regret it now because a couple years after that he just suddenly died one day. He seemed kinda depressed before he died. I really think he just let himself go. The alcohol and the bum arm and the depression and not having anything going on in life, all of that together sent him to an early grave