He said to interviewer, "Could you please repeat the question?"

In direct and indirect speech, when we report someone's request, we often use the verb "requested" followed by an indirect request. The structure of indirect speech for requests is typically: "requested + [indirect request]."

In this case, the original sentence is a polite request: "Could you please repeat the question?"

The correct indirect speech transformation is: "He requested the interviewer to repeat the question."

Therefore, the correct answer is Option C: He requested the interviewer to repeat the question. This option accurately conveys the original request in indirect speech without unnecessary additions or alterations.