Welcome to Q&A forum,I am glad that you can discuss some general issues of OneNote with us.
But so far, OneNote does not have this function to merge notebooks.
You may try to copy all notes you need to merge, and paste them in Word. Then copy back to one page in Onenote.
Besides, you may also try to create a quick table of contents to other areas in your notes. More detailed information, please refer to "Create links to notebooks, sections, pages, and paragraphs".
In OneNote for UserVoice forum, there is a similar thread "Merge Sections in Notebooks". Please vote up it to let the development engineers of OneNote hear your voice louder.
Thanks for your understanding.
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