First we’ll start by grabbing your WorkshopID, Your collection id is the numbers after the id= in the Collection URL so if my collection is http://steamcommunity.com/sharedfiles/filedetails/?id=99999999 my WorkshopID would be 99999999.
Now that we have the WorkshopID you will need an Authkey, You can obtain one here: http://steamcommunity.com/dev/apikey
(Use your Server’s IP as the Domain)
Now that we have both our WorkshopID and our Authkey we can add the collection to the server.
Start by navigating to your CommandLine Manager in the Game Panel
Then add your Authkey to the Authkey field and your WorkshopID to your WorkshopID field
Now click save and restart the server and you will have your collection added to your server.