You can now edit both saved and published works on the new app (from version 4 and above) by following these steps:

Launch the app
Log In

Go to Create
Scroll down to Edit Another Story as in the image below:

Once done, you'll find all your published books and Drafts as in the image below:

Click on the book you would like to edit to start editing it.
Once done, click on Publish on the top-right corner of the app.