Turning the interior LED light on or off is an easy yet subtle process. There isn’t an oldskool switch, but there is a touch-switch on the light itself. The small dent/notch on the light is the switch. Touch it gently and the light will go on or off.
See this how-to video for more info about using the interior LED light - all Spaceships campervans have the same interior LED light system. It starts at the end of the set-up of the bed segment and right before the awning demonstration, see the timeline of the video for chapters and their name.