1) Unscrew the nut using an 11 or 12 mm socket wrench. Remove the nut and immediately discard the nut if it has a plastic washer attached to it. The adjustable angle sensor has a break-away feature inside the nut which is used to set the torque on the screw. This is a one time use feature. For this reason a nut with a plastic washer cannot be reused.
2) Remove the sensor and valve from the rim and inspect the sensor for any physical or sealant damage.