I’m a little confused by your question. You’ve created a single page with multiple content areas but you want to edit those content areas separately?
What you should have is a custom post type that will have the content for each page and then use a repeater with post object fields or a relationship field to allow the pages to be selected for inclusion on your single page.
There wouldn’t be any way to pull the content already entered for the single page post into separate editors.
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