I can't change a header

You have Global header settings here

https://www.awesomescreenshot.com/image/3167342/7976d7ee0d0e531d024ae001234a3997

and it applies for all headers if you have Default option on the page here https://www.awesomescreenshot.com/image/3167348/6e6e62657db187107c12613224c27072

If you choose Header1 - 5 it overwrite Global header option on this page.