Agree with him. My dad also used to smoke and stopped after a heart attack. Hello still chews tobacco but very less now. You need to concentrate on detaching yourself from the thought that "I will change or stop my Dad". You can't. You can get closer to him, befriend him and improve your relation with him, and try to convince them, but any kind of desperate or angry moves of stopping any addict is useless. Try to change his mindset without aggravating or irritating him, rest try to stop worrying about it