Make edits to DNS settings on two or three domains

General information for the website: not applicable - see requirements
Description of requirements/features: I have a sub-domain setup ( reporting.reputationdata.co.uk ) which hosted with wpxhosting.com

I also have access to a web-based tool that runs reports. That runs at this domain ( reputationdata.repgrader.com ) .

A screenshot is attached of the instructions the tool offers.

The domain is registered at names.co.uk

I am having great difficulty setting things up so that people visting reporting.reputationdata.co.uk will see the content on reputationdata.repgrader.com . I also want to keep reporting.reputationdata.co.uk in the browser url for branding purposes.
Extra notes: