How do you get the Low Tire Indicator Idiot light to go out after replacing a tire due to a flat?

There are two ways to reset the indicator light - the first is to hold down the button (hidden under the dashboard next to the steering column) until the light goes out. That's a reset. There's also a reactivation, you hold the button until the light flashes three times and then release, that's for use after a wheel is changed, etc. Make sure they have done the reactivation, not just the reset.