Hi there
My suggestions:
1. Ask your advisor, PI or colleagues from your former department to review in relevant journals. For example, the journal of Ethnic and Racial Studies always publishes book reviews, as do many other journals. Similarly, reviews are sometimes published in more mainstream media like Jacobin, e-flux, etc.
2. Reach out to other scholars working in a similar field. Perhaps there's someone you cited a lot or who is doing research on a similar subject? Again, they might be interested in critically engaging with your work.
3. Get your book on a syllabus or two. Contacting friends who are teaching and see if they'd like to include a chapter, join a Facebook or social media group for researchers in a similar field and make a free copy available to them. The more your book circulates, the more likely someone will want to review it.
But what do I know, I'm not even in a PhD program.
Good luck!