There are two locations I know of that control the lights.
Firstly, if you tap on the headlight indicator, a small “card” should pop up with a couple of buttons for lights. Fog and auto-high beam should be next to each other, above the off/parking/on/auto options for the headlights.
On the other hand, if you tap on the car icon at the bottom left and then go to lights, it’ll be below the off/parking/on/auto options for lights.
So that’s that for the button.
(Auto) As for it being on, it is on when the headlights come on, in auto, of the fog is set to on.
(Parking) I know that when I get home and switch my headlights from auto to parking (so I don’t shine my headlights into the house across the street as I back into my driveway), the fog lights stay on. I don’t recall checking if they’re on if I start with the headlights set to parking.
(On/Off) Of course, they should be on or off to match, if the headlight is set to on or off.