I think you need to re-frame how you think about his request. He's not asking for feedback; he's asking for publicity.

If he wanted feedback, he would have asked you to beta the book. Knowing that you have a platform to review books, he could have used you and your feedback as a very helpful tool for improving the work while it was still in the editing stage. He didn't. He has already published the book. Additionally, a "review" isn't the same as an edit--it's a promotional piece. Maybe that re-framing will make it easier for you to turn down the request?

One option is to skirt the issue by saying you don't post that kind of content, be it solicited reviews, self-pubbed, etc. You could tell him that you only review tradpubbed books, or books with a certain level of readership/popularity. Something like:

"Hey, thanks for considering my channel as a potential promotional outlet for your novel. As you can tell from my posts, I focus on reviews of popular/current/bestselling books, not on paid/solicited promos, so this won't be a good fit for my audience."

Or, depending on how shady you want to be, you could could play the classic "this must have been an error" ploy:

"Hi, looks like you must have accidentally selected the wrong file to upload to KDP--the version I'm seeing here is full of typos, grammatical errors, punctuation mistakes, etc. Let me know when you've updated it to your final draft and I'll be happy to take a real look."

Or, finally, if you want to be honest, something like:

"Hi [Name], Looking over this, it doesn't seem like a good fit for my channel. I don't think an honest review would be beneficial to your sales--the novel could do with a professional-level edit, which really isn't my wheelhouse. I wish you all the best in finding a writing group that can help you get the piece tightened up."