Youtube Video Link how to Change themes and icons in KDE Plasma
path to breeze-theme default user icon
The icon you are looking for could be available here:
The use of paths in a .desktop file
Icon field is the icon that should be used by the launcher and represents the application. All icons that are under the directory
/usr/share/pixmaps don't need to have their full path specified, but their filename without the extension. For example, if the icon file is
/usr/share/pixmaps/wallch.png, then the Icon field should be just 'wallch'. All other icons should have their full path specified.