Which “page” are you currently looking at? The page where the dynamic data is saved to, or the header template?
If you’re editing a page that has the data available: deselect the element. If it’s selected, it will always show its content (not the dynamic data).
If header template: choose a page in populate content settings that has this dynamic data available. Otherwise, the dynamic data tag can’t retrieve any data since it doesn’t know from where.