When I try to reinstall the Server App it just shows installed and the date it was purchased. How can I reinstall it?

I bought a Mac Mini Server and after set up I realized that it was not set up as a mirrored raid system. So I followed the instructions on how to do that - this erased my drives. Restarted and reinstalled the Mountain Lion software but when I go to the app store it shows the server sotware in my purchases but there is no option for reinstall - it just shows INSTALLED and the date it was purchased.

Ho do I reinstall my server app?