» How do I place this on the default login page?
C5 Extras > Support > Knowledge Base > Register User Pro > How do I place this on the default login page?

You would have to edit the Login page because it cannot be edited directly via C5. The file to edit is usually found in this path:

concrete5_root/concrete/single_pages/login.php

And add the block in by hardcoding it on that file. Here is an article on how to add a block by hardcoding it.