Need some help...

I can't figure out how to install 3rd party content. Any advice?
https://www.railworksamerica.com/forum/
https://www.railworksamerica.com/forum/viewtopic.php?f=29&t=7084
BigBoyMoon wrote:IT keeps coming up in red, and saying I'm missing assets. I'm trying to install the GreatNortherner's SD7.