In order to load a book that you have worked on in the past, you must have saved it inside of the Book Bolt Studio.
These are saved in the cloud, and should be available to you no matter what computer you are on.
To load a previously saved book, simply go to Project in the top menu bar here:
Under project, select “My Projects”
Here, you can search for previous books that you have worked on in the search bar, or simply click on the book project that you wish to load:
This will then load in the previous book you were working on (so make sure you save your current book!)