My search is leading me no where :( At first I found this page, which sadly assumed the studio tank was already there and dived into config cloning.
https://support.shotgunsoftware.com/hc/en-us/articles/219033168-Configuration-staging-and-rollout
Then I found this page which says "First you need to let us know that you want to enable Tank on your Shotgun Server. We will carry out the necessary steps and send you a set of license keys. But if you are reading this document, you have probably already completed this step!".
What exactly is "let us know"? Do I email Shotgun support asking to use tank?