Mine's a 2004 car. This warning comes on for me nearly every time the wheels come off, but some time after. No idea why. Anyway I've had to use the reset a few times. The button's under the steering wheel but it's nearer the pedals than the steering wheel! You've probably just not looked far down enough! There are instructions in the manual if you have that, but basically you have to press the button once to reset, then press and hold until you see the 'initialised' message,