1. On your iOS device, open KyBook3
2. In KyBook3, tap Control, tap Content Server, tap the Activate switch
3. In this plugin, click Configure and enter the Link, Username, & Password from step 2
4. In KyBook3, tap Library
5. In this plugin, click Synchronize with KyBook3
6. In KyBook3, tap Control, tap Cache, tap Clear space under BOOK COVERS CACHE
7. Shutdown and restart KyBook3

For more info, visit https://www.mobileread.com/forums/showthread.php?t=316347