Adding mods is a well documented activity for ARK. It will depend on how you are running a server. If you have rented a server, go to the server provider's help pages for info on how they update their Ark server.

If you are running a local single player, you will subscribe to the mod here on Steam first. When you are loading your local server, you should have a list of mods you've suscribed to on to the right of the button you use to start the server. Pick the mods you want top run and start the server.