1. You have to apply to the Registrar of Births and Deaths in the Municipal Corporation for rectification of errors in your birth certificate. A copy of your other documents of identity such as aadhar card, voter card and matric certificate wherein the accurate date of birth is mentioned should be annexed along with the application.
2. The fact that you delayed applying for rectification this long may result in rejection of your application, in which event you can go to court to seek its directions to the registrar to carry out the rectification.