You take it to a authorized service center, or a watchmaker you trust. There have been many movements and models in VC’s long and storied history. Unless the fake is terrible (a supposedly new watch with a bunch of misaligned features, crooked text, plastic pieces, etc.) it could be difficult to spot.
The good news is VC watches are faked much less than other luxury brands like Rolex. You have an overall better chance of the watch being genuine, but that doesn’t mean it is.