There's no known way to turn a chimera back to its original form. It's not something that can "heal" with time, either.

I assume it would require powerful magic, or a specific scientific or medical procedure... perhaps a combination of all of those things. Something that hasn't yet been developed in any of the places I've visited.

The most promising lead I've followed is something known as the Claire Bible... a collection of otherworldly knowledge, things normally known only to gods and demons. It's said that the information it contains is nigh-infinite. But it's extremely rare to find even a scrap of a manuscript... Such knowledge has the power to change the course of history, so the higher races strive to keep it out of the hands of mortals.