I have L1A(Blanket) visa interview on 9th July at chennai. However just realized that the DOB filled in I-129 has wrong date.

At the interview point out the typo. The Consulate will follow your passport. Mr. Smith is an attorney with over 25 years of immigration experience with complex immigration issues and successful filings. 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. Smith's statement above does not create an attorney/client relationship.

Did you put the correct information (which should match your passport) on the DS-160? If so, don't worry, you can talk to the officer about fixing that ... assuming it is a simple mistake/error. Some of us are going to be working all weekend, you may want to contact an attorney for a Skype consultation. Just click on a name and follow the link for sending a private e-mail.

Go ahead with the interview, let the officer know about the mistake. Everything should be fine. All the best for your interview.