How to redownload audiobooks on iTunes for Windows
Open iTunes.
From the menu bar at the top of the iTunes window, choose Account > Purchased.
If you use Family Sharing, you'll see Family Purchases instead of Purchased.
Choose Audiobooks from the menu of the iTunes window.
Find the audiobook that you want to redownload.
If you use Family Sharing, you can choose a family member's name next to Purchased to see their purchases.