Hi there,
So pretty much my main headings for post and pages can’t be re edited once they’ve been created and I click away to another part of the page.
If you’re pertaining to the layout of the header, you’ll have to edit it by looking for the Block Element that’s responsible for it on Appearance > Elements.
As for the actual content values that are fetched, that’s taken from a post (title, post meta, etc). It’s dynamically set.