First, remove the cover by unscrewing the 4 screws holding the cover in place.

The flame sensor is located in the center-right area of the heat exchanger. (Marked with blue tape)

Unscrew the silver bracket holding the flame sensor in place and set the screw(s) aside in a safe place.

Replace the flame sensor with the new one. Be sure it’s over the flame.

Screw the screws back into the silver bracket, put the cover back on and activate the water heater.