You maybe aimed to address your question to the Research Gate moderators, but it is placed instead in the section "questions" addressed to all the Research Gate users. Let me try to answer it.
In the list of your contributions, below each contribution there is a line with buttons "Add full-text", "Add to project", "Add supplementary resources" and a small down-arrow. When you press on that small arrow you see the option "edit". When you select that option you will be able to change the type of publication and everything else. It looks like on Research Gate there is no type of publication "Book review" (at least I did not found it), but you can select some other type, say "article" and to write in the Abstract that this is a book review (and to give a reference to the corresponding book if you like).