If you're looking to re-install your game server, you can do so by navigating to your game server, via the Game server overview page.
Navigate to the Danger zone tab, in the tab menu.
To confirm the action, you are required to enter your password. This is the password you use to login to GameserverApp.
Once activated, it will take between 10 - 20 minutes for the game server to re-install. All progress like savefiles, config files and mods will be automatically restored for you.