Okay, but where is your server located at? In a datacenter? Inside your company?
If it is in a datacenter, you just need to ask the datacenter's tech support to configure the reverse DNS of your IP to whatever hostname you need.
If it is inside your company, that is usually done by the link/IP provider or the person responsible for network management inside your company, normally the one taking care of DNS servers and/or IP delegations.
Cheers.