How can I create my own “register” page? or edit the current page?

I’ve installed TMI, but it seems they are using the parameter instead of generating additional pages. I am good with current registration page, but there are mistranslated word(incorrect localization) on the word (username)

(The user complains that TMI does not allow to use “ko-KR” as a username.)

So, I prefer to add some text into the register page, but I could not found how to access/edit the register page.

Please help!

The page I need help with: [log in to see the link]