You have to make a distinction between plagiarism and copyright.
Plagiarism is about attributing the source of an original text and relates to academic integrity. As such, even self-authored work need to be cited and quoted to avoid plagiarism. Applied to your question, assuming the novel has been previously published, it would constitute plagiarism to rewrite one’s own work without citing and quoting the original work even if written by oneself and irregardless of an AI’s help. If the novel has not been previously published by you, no one would be able to accuse you of plagiarism. So it becomes a personal ethical choice whether to cite or quote oneself from an unpublished work. Most academics still cite oneself even if the work is unpublished because it could create problems later on.
The use of an AI to edit the novel is an altogether separate ethical issue. There is now a consensus that standard ethical practice requires the author to disclose the use of an AI for editing or writing- most publishers will require such disclosure.
As for copyright, that is an altogether separate legal analysis. First, an AI cannot own a copyright for the primary reason that an AI is not a legal person- a requirement for copyright protection. The next question then is whether the novel meets the copyright test of originality, fixation, expression, authorship, and subject matter. Assuming the novel meets the copyright test, there is the question of who owns the copyright- the author, publisher, or both.