When considering what you could write for a book review on The Witch of Blackbird Pond, you'll need to take your teacher's guidelines into account. What is the book review supposed to focus on? If it has a specific focus, that's where you should put your efforts. If the book review is supposed to share your own personal responses, you'll need to read the book and explain what it means to you and how it made you feel.
However, if the book review is more analytical in focus, you could start by reading the enote study guide on The Witch of Blackbird Pond. It will help you understand the historical context and origins of the work, the themes, and the relationships among the characters.