Instructions for installing Extra Flags are at the link below:
https://flagtism.gitlab.io/Extra-Flags-for-4chan/
To add flags to the repo if you've been given the rights:
- Pull most recent master branch to prevent conflicts
- Copy desired flag PNG files into the proper folder locations
- Run php/flag-lister.bat if you use Windows, or php/flag-lister.sh if you use GNU+Linux
- Commit changes and push to master branch