Download the required files here.
Save the downloaded folder “404-files.zip” on your computer and Unpack the downloaded folder.
Upload the file 404.php to your child theme folder.
If you don’t have a child theme you have to create one first. You can follow this tutorial How to create a Divi Child Theme to create one.
In your WordPress dashboard navigate to Divi > Divi Library.
Click on “Import & Export”
Import the json file 404 page layout.json
You can change the content to your likings, or you can delete all the sections/rows/modules and create something new.
This will not work with the visual builder so you have to edit it from Divi > Divi Library > 404 page