Since Ewebot theme version 2.5.9 all theme options have been moved to WordPress Customizer. This way the user can see the live changes for the global settings.
To have a custom 404 page, please do the following:
- Create a regular page in Elementor page builder
- Add any content that you wish to have on that page
- Assign that custom 404 error page in Appearance -> Customizer -> Theme options -> General