That is the switch that turns the courtesy lights on and off, also does the "door open" warning on the dash, and also does the alarm.
Its a push to turn off, but often get dirty, plus over time, the movement can snap where the wire joins the terminal.
Spray the screw with wd40 fo a couple of days, then you will be able to undo it, and remove the switch. Often some contact cleaner will fix it, if not someone like Banshee may well have a spare.
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