I had a surgery 4 years ago. I had my 4 wisdom teeth extracted and until now, my lower lip is still numb and I feel prickle in my lower lip and chin. What should I do?

Sometimes. Due to location of the nerve in the jaw this is sometimes a side effect of removing wisdom teeth. Their may or may not have been any way to avoid it.
Paresthesia. This is most likely related to paresthesia. A condition associated with nerve damage. Your case appears to be of mild damage and does not require surgery. After 4 years i would nit expect for you to have a change in symptoms.
Nerve Can Regenerate. As a dentist, who had a similar experience after a different dental surgery (apicoectomy), i can relate that after 3.5 years the feeling began to return as tingling and progressed to itching and finally today I have totally normal feeling back in my lip. It is almost like when you get dental local anesthesia where you are totally numb and when it is wearing off, you get a tingling feeling.