Are you electronically inclined?
The LED lamps are almost never intended to be replaced by the end-user. You'll need to open it up and probably solder a new LED in place.
... or tolerate it as is.
Google "Super Bright LEDs" there is an (albeit crappy) online store that I've ordered from several times that sells the types of LEDs found in these fixtures. You may want to go ahead and replace all of them while you're at it so they all match.