The new page header add-on is part of GPP 1.4 which is currently in Release Candidate (stage after Beta) – so unless you install the Beta versions you wont see this function yet. I believe Tom is looking to release 1.4 very soon.
If you want to test the Beta (RC) version – on a development site – then the how to is here:
If the code is active (i use Code Snippets to add and activate the code) – then it might just be a timing thing. Some people state that it can take a while for the update to show up.