rDNS (ptr record)

I am an uble yo set up my server with a reverse DNS lookup. My server is having a public ip address with 196.188.x. x and this server is having a private ip address of 192.168.x. x. When i prompt dig -x 196.188.x. x it is replying that a mismatch has occured and responding that the server got a reverse lookup for the private ip address. Which is meaningless for me. Any one help me up set the rDNS record for my public address please. If there are also any recommended suggestions.