The settings optimization is done fully automatically when you start a game that has support for it, you don’t have to do anything. Not all games have that though. Whenever settings are changed for a game, a notification is shown that advises to restart the game. Check this blog post for a short video about it. You can see what Direct VR features (if any) are available for a game on the Direct VR page of the vorpX ingame menu.
For games that do not have automatic settings optimization or other Direct VR feature support please check the Essential Hints Guide in the vorpX help. It explains possible workarounds in regard to FOV which vary from game to game.