On our 2018 Aria it is right inside the door above the House Batt switch. It is labelled STEP and has ON and OFF positions.
It took me some digging to discover that ON means to DISABLE the automatic extending and retracting of the steps every time that the door is opened and closed. When set this way, the steps will stay extended until you turn the ignition on.
Turning the switch OFF will cause the steps to extend every time that the door opens and retract when the door closes.
Ours has been a bit flakey since day one, most likely because the magnet on the door doesn't quite line up with the sensor mounted to the door jamb. We can make it work most of the time by closing the door slowly.
__________________
|