This is a special YaST module that allows users to configure pre-installed systems to match their needs, e.g., language, network settings, root password, etc.
See:
The workflow is defined in a control file, which uses the same format as the Installer control file. The default control file can be found in control directory.
More subject-specific pieces of information can be found in the doc directory.
This module is developed as part of YaST. See the development documentation.
To get the source code, clone the GitHub repository:
$ git clone https://github.com/yast/yast-firstboot.git
If you want to contribute into the project you can fork the repository and clone your fork.
sudo systemctl enable YaST2-Firstboot.service
sudo touch /var/lib/YaST2/reconfig_system
If you have any question, feel free to ask at the development mailing list or at the #yast IRC channel on libera.chat.