Make sure he brings a certified copy or a original of his birth certificate so the correction can be made at the interview. You can also email the consulate's immigrant section and explain the problem to them.
Guerra Saenz, PL--Immigration Attorneys (954) 434-5800. This answer is of a general nature and should not be relied upon as final, nor is it intended as legal advice.
Do your best to correct the problem either before or at the interview
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He should bring his birth certificate to his interview.
(213) 394-4554 x0 Mr. Shusterman is a former INS Trial Attorney (1976-82) with over 35 years of immigration experience. His response to your question is general in nature, as not all the facts are known to him. You should retain an attorney experienced in immigration law to review all the facts in your case in order to receive advice specific to your case. Mr. Shusterman's statement above does not create an attorney/client relationship.