How to navigate using old work?

I recently completed and submitted a master’s thesis.

My university only allowed me to use secondary research which was honestly extremely disheartening. It also only found out half way through so I felt like my thesis was no longer my own in a sense.

I am really passionate about this topic and really want the opportunity to complete this research on my own terms and perhaps investigate publishing it independently later down the road. The research on that will come later.

My question for now is, how do I navigate rewriting the literature review? Of course it can’t be reused because it would be self plagiarism but the only thing that needed to change about the paper would be chapters 3-5.

Has anyone had an experience like this? How did you navigate having to start from scratch any rewriting all of the relevant content from your lit review into something completely new even though the content is essentially the same? I’m having a hard time trying to undertake it.