Sub caste change

A person join a service as a SC(sub caste-patni) candidate in 2013 but, now he knows that he is not SC(Sub caste-Patni), actually he is SC(Sub caste-Namasudra). May I know that, it is possible to change his sub caste to his actuall sub caste within same caste; whenever it happen due to sum miss knowledge. He is afraid to know that he does an illegal things. Sir reply please......