Resetting a tire pressure sensor varies, depending on whether the sensor is part of a direct or indirect monitoring system. Direct monitoring systems are more commonly found in the U.S. while indirect monitoring systems are more common in Europe.
Resetting a direct monitoring system can be far more simple, since it may require that you only press a single button. This button is commonly located on the dashboard. However, it is best to consult your owner's manual, or an online manual, to determine where the button is for your particular make and model of vehicle.
To reset an indirect monitoring system, you may need to use an additional tool, such as a magnet. This also may require that you press a button located in the glove compartment. Again, this will vary depending on the make and model of your vehicle, so consult your owner's manual.
In both the case of a direct and indirect system, make sure that all your tires are properly inflated and that the battery powering your monitoring system is not dead, since these factors will affect your pressure sensor. You may also need to use the magnet method. In this case, press both the lock and unlock buttons on your key fob until your car chirps once. Then, take your magnet tool, and place it over the valve stem on your tires. Go clockwise, beginning with your front left tire. When you place the magnet to the valve stem, don't remove it until you hear your car alarm chirp, once at each wheel.