The Remixer generates "transcluded" pages that mirror the original Master content. To edit the content on the new Remixed page, authors have to either edit the original material (e.g. with errors) or have to "fork" the page to copy the content from the original master page into the the new Remixed page.
When and How to Edit Original Page
DON'T and if the system lets you, as a newbe, there is something wrong. Back away slowly and send an email to Info@libretexts.org, but what you can do is
Create a Copy of the Original Page to Edit
If you are altering the content of the original page to fit into a different flow than the original book, changing the pedagogy of how the material is presented, deleting subsections, or otherwise majorly modifying the original, you will want to "fork" the original page. Forking a page creates a copy of the original page in the new location that is completely independent of the original and you can edit it as you see fit (without affecting the original source page).
The easiest way to do this is with the "Forker" which works automatically by pressing the icon next to the remixed (and transcluded page). Then authors can edit the remixed pages without affecting any other page on the platform. The downside is that any upgrades to the Master content will not be reflected in these forked pages but by using the star on the third line below, you can be notified of changes