Hi, Steve.
A confusion did happen at some point, and this button was removed in 3.1.3 as a result. More on this in [this issue](https://github.com/GluuFederation/oxTrust/issues/808). It will return in upcoming 3.1.4 package, with some enhancements. Atm the easiest way to register a protected resource will be using [this command](https://gluu.org/docs/oxd/3.1.3.1/api/#uma-rs-protect-resources) (if you employ our oxd server in your environment).
I'll update docs for 3.1.3 to prevent further confusion.