Did you run the game at least one time before using the optimizer? I would assume that this is necessary for the game to be able create the .ini files first. Using the Steam version too here (I don’t think there is another one), so that can’t be the issue.
If the auto optimization continues to fail for some reason, you can also adjust the FOV manually (googling for “Bioshock Infinite fov” should reveal a few tutorials). Unfortunately for BSI that’s a bit more complicated than for most games since the FOV has to be calculated as an offset, but that’s also explained in most tutorials.