Step 1: Login to your client area.
Step 2: Go to, My Products & Services and here all of your services will be listed.
Step 3: Open the service.
Step 4: Now, scroll down and you find the following:
Step 5: To apply rDNS, click on "Configure Reverse DNS". And you will find the following options:
Step 6: Press on edit under "configure".
Step 7: Now enter hostname associated with each IP and then save by clicking on "set Reverse DNS".
Note: If you don't find the rDNS option under your product & services. Kindly open a support ticket.
That's it !!