I m smoking from past few years but before 2 or 3 days some white spots appeared under my lips, so what should I do to get rid of these spots?

Need to be evaluated. You should have an evaluation performed by your dentist to determine what the white spots are, and what treatment should be provided if any.
See below. Symptoms and concerns like these mandate a thorough evaluation by your doctor. Only after such an evaluation, which may include labs and radiographic examinations, can he/she let you know what's going on and how best to help you.