date of birth change

i want to change the dob of my child becoz of the school reason . i hv already make passport with the original date of the baby but due to school admission i made a birth certificate so now i want to change the dob in passpoert according to the certificate. now the problem is that i told the agent to do so he applied the passport in tatkal service by change of dob. now the agent says the passport come under hit. so pls tel me the procedure hw do i proceed further i am ready to surrender the old passport pls guide me.