Step 1: You will need to determine if the pedal in question successfully updated the firmware. A pedal that fails to update appropriately will not display any lights and will appear unresponsive. Another indication of this state is that the pedal will not connect under "Virtual Bike" in the PowerTap Mobile App.
Step 2: Do not worry. Your power meter is likely temporarily stuck in pedal purgatory. Follow steps 3-5 below to revive your pedal.
Step 3: Make sure the Bluetooth (BLE) setting on your iOS device is set to "on."
Step 4: Once BLE is activated, go to the "Settings" menu in the PowerTap Mobile App.
Step 5: Instead of tapping "Bike Set-Up," scroll down and select "Recover Firmware." From there your iOS device will pull your pedals out of purgatory and get them up and running again.