If you've been through the process of importing an image, video or file from your Google Drive, you will have linked your Book Creator account to Google Drive to do this.
Sometimes you might find you want to access a different Google Drive account, or revoke access altogether.
To do this, you need to go https://drive.google.com/drive/my-drive and click the Settings icon, then Manage Apps. You'll see Book Creator there. Click on the OPTIONS dropdown and disconnect it.