To access the books you already downloaded is very simple: on the home screen, just touch the Astronaut to enter My Space and your books will appear in the section Available Offline, as in the images below.
If you can not find the book you are looking for, there are two things:
- It was downloaded with another profile. Tap the Swap Profiles icon and choose another user to see if that's what happened.
- The book is still downloading. Then just wait a bit to enjoy the story.