You will have bought it from RSSLO. Don't the instructions that came with it tell you what to do? It requires the following payware from RSSLO, do you have them? Arlbergbahn Route ÖBB 1042 Taurus – ÖBB 1016 Vectron ELL Wagon Pack 01 Wagon Pack 02
I don't have this scenario pack, but all the RSSLO packs I have are .exe files. Assuming it works the way of their others, you just need to click on the .exe and it auto executes. It will then ask you where you want to install it (be careful the default is a Railworks folder on the C: drive). Next you have to enter the activation key (found on your RSSLO account). Then it installs and you're ready to go.