It should be dealer reset when the tyres have been fitted although it may need a second reset as they bed in. No idea why but the warning light sometimes comes on spontaneously a few hundred miles later but for no apparent reason. Checking the tyre pressures shows that they are all "normal" - ie. set to exactly the same pressure by the dealer. (which isn't right but isn't too disastrous either)
Most times I have checked main dealer or quickfit pressurised tyres they have all been inflated to the same pressure midway between whatever the front and rear axles recommend though sometimes a bit on the high side.
I wouldn't put it past them to inflate all tyres to the same pressure...