What should I do if I do not know the answer to the interviewer’s question?
It is absolutely normal for you to not know the answers to all the questions that the interviewer asks. Even the interviewer doesn’t expect you to know all the answers. When you don’t know a particular answer just admit it. Giving a truthful answer is always better than beating around the bush. What the interviewer is testing is your ability to admit the fact that you do not know the answer to that question.