What reverse DNS is
Ordinary DNS turns a name into an address. Reverse DNS goes the other way: for 192.0.2.10 a resolver asks for the PTR record of 10.2.0.192.in-addr.arpa, and for IPv6 for a name built from the 32 hex digits of the address under ip6.arpa. The PTR record is controlled by whoever holds the address block, usually the hosting provider or ISP, not by the owner of the domain. You set it in the provider's control panel or by asking them.