Error Unable to find existing config
This error is not critical. This is a warning; When you've first installed the game you may not have a main configuration file for the game, some games only generate this file when started for the first time. Once you press save at the bottom of your "Settings" submenu for your game instance, you will see a 'Success, saved config file.' and the warning will go away.
This error appears when there is an issue on the config file, an invalid name, file permissions issue etc. If you are unable to resolve this error, do not hesitate to contact support via your "Support" menu.