If you need to add new content to a boxset you've already started in Atticus, you can easily do so by saving the new chapter or group of chapters in a .docx file and importing it into Atticus. Here's a step-by-step guide:
In Atticus, navigate to the book where you want to add new content.
Look for the three dots located next to the 'Add Chapter' button.
Click on the three dots to open a menu of additional options.
From the menu that appears, select 'Import Chapters' and select your file.
When you see the prompt 'Do you want to import chapters into a new Volume?' Select 'Yes'.