Check to ensure your book is “Live” on your KDP Bookshelf. If your book still says "Draft", you’ll need to submit it first and wait until it is approved and live.
Find your book on the Bookshelf and click the ellipsis button (the three dots) next to it. This opens up a dropdown menu. Then click on the option: Order Author Copies.
Determine the Number of Copies you want and enter that.
You will receive an email once you have requested to order author copies, which you will need to open to complete your order.