Select the A New God tile, then New Game to begin playing.
If you cannot locate the A New God tile, please make sure that the DLC is installed.
Fenyx will have all of their abilities unlocked, so that you can begin A New God, even if you have not completed the main game.
The DLC save files are seperate from the main game saves. This means your progress in the main game will not be affected at all when you start the DLC.
If you have any other questions, please get in touch.