How do I change my caste from my father’s to the mother’s caste?

It is not possible to change one's caste under Indian law. Caste is a fixed feature of an individual's identity that is determined at birth. A person's caste is derived from their father's caste and is established by their place of birth. 
But in February 2021, the Tamil Nadu government issued an order allowing children born to parents from two different castes to get a community certificate that lists both parents' castes. The order states that parents may decide to declare the caste of their child based on the caste of either the mother or the father. It's crucial to remember that this order solely pertains to the state of Tamil Nadu and might not be applicable elsewhere in India.