Insert a coin, screwdriver, or other tool in the indention on the side of the RPM Speed sensor to pry off the top face plate.
Remove the battery and replace it with another CR2032 coin cell battery.
Place the lid back on the Wahoo SPEED. Make sure the rubber O-ring is properly seated and the two posts on the bottom of the sensor are aligned with the holes in the face plate.
The face plate should snap back into place, making a complete seal with the bottom of the sensor along the outside perimeter. The LED light should blink, indicating that the battery is correctly oriented and powering the sensor.