The phrase "to accompany the book" means to go along with or be included with the book. It refers to something that is meant to be used or experienced together with the book. Full definition
And, check out her below how - to video which accompanies the book. (idealhome.co.uk)
Online videos that accompany the book bring the text alive by showing readers what coaching looks and sounds like. (stenhouse.com)
Make it known that if someone buys your eBook, they can get a free accompanying book or soundtrack or poster, whatever is of value to your target audience. (chadwickcannon.com)