If you haven’t done it at all or any IEW you might actually want to start with Book 1 The Nose Tree. It introduces kids to the IEW format of labeling things. We did that last year with my 5th, 7th, and 8th graders and I just had them do more than one sentence per day since they were older. Once they have the basics down you can move on to other levels of books. Just my opinion!
They also have placement tests on their website and you can contact them as well to see what they recommend 