The first step is to splash rack it, I mean break every “be gentle with your wine” rule. If it is a mild case it will blow off. Next step would be a product called redulees and then if all else fails, copper sulfate. Copper sulfate is the hammer, but must be used with caution as to not leave heavy metals in your wine.
H2S is not something that will go away on its own in my experience, it needs to be addressed and the sooner, the better or else it will deteriorate the wine pass the point of no return.