Set Reverse DNS Entries in Core
Log into your CORE account at https://core.hostdime.com
Click on Dedicated Servers under Products
Click on Details icon for the server you would like to modify the reverse DNS entries for.
Click on Reverse DNS Entries near the top of the page.
Edit the Value column on the IP address you would like to modify the rDNS record, then click the check (✓) icon to save the record for that IP.