Whereas a regular DNS lookup resolves the IP address for a given domain name, a Reverse DNS lookup achieves the opposite: it resolves the domain name for a given IP address.
To change the Reverse DNS for any IP of your Alwyzon virtual servers, login to the client area and visit the server management panel for the server whose IP you want to configure. In the upper right corner of the server management panel you should see a "More" dropdown. Open that dropdown and select the "Reverse DNS" menu item. You should then see a modal appear which allows you to set a new reverse DNS entry for your IP address. Please be aware, that any changes to your reverse DNS entries may take up to 24 hours to be distributed.