This quest is not available in game.
Retrieve the Cloven Hoof for Rau Cliffrunner at the Freewind Post.
Using the water you brought, you will be able to temporarily douse the flame that holds the centaur relic. It will not work permanently, however, so you will have to be quick about it.
You will find Splithoof Crag, the centaurs' stronghold, to the north of here. The flame is kept in Splithoof Hold, a heavily guarded part of the crag.
Be careful, though, the Galak centaur have great numbers here, and will be rather reluctant to surrender something so dear to them.