You must own the RSC DLC Challenger pack 01 available from Steam in order to use this repaint.
Install the RWP using the TS2013 Utility program found in your Railworks folder.
When completed you must manually copy the ALL GeoPcDx files from the default Challenger which is located in Railworks\Assets\RSC\ChallengerPack01\RailVehicles\Steam\Challenger\Default\Engine
and copy them to Railworks\Assets\RSC\ChallengerPack01\RailVehicles\Steam\Challenger\NERW\Engine
You must also copy the GeoPcDx file for the tender GeoPcDx file to the NERW tender folder.