Mr. Srinivas Hegde ji,
I think in Karnataka DOB mentioned in SSLC Marks card isconclusive evidence for all future documentation. Still you want to rectify the DOB you are required to go the origination of your DOB ,which is primary school.
Go to primary school where you registered as a student for the very first time. The School Master gives you a certificate evidencing the date of birth entered in the school record. Then Notarise the same before magistrate/Notary public and submit the same to the concerned authority with an application to correction of DOB. As I understood,they may give you duplicate S S L C marks card with correct DOB by retaining original one.