With respect to the OP’s question, we usually don’t. Why would we? Eucharistic miracles are, please pardon me, pointless to a non-believer. What does it accomplish? What does it matter to me if a piece of bread is said to have turned into human tissue?
I would say, “Hmm, that certainly seems an odd thing to report. It’s likely a mistake in either the lab sample, the process of preservation of the lab sample (such as contamination, etc.), a defect in the equipment, or a misidentification by the lab worker.”
And then it would go no further, because it isn’t the kind of “miracle” that makes any difference to me. Why do I need said thing to occur, or why do I need to have dead people be shown to have a very slow decaying process? In the end, they are still dead. And the Eucharistic sample is still just a collection of cellular material.
A useful miracle is one that one that simply cannot be explained by any other possibility.
Such as, you take a randomized group of people who are dying from ALS and give some the Eucharist and others a regular cracker, and find out that those who were in the first group had a complete and full restoration of all neurological function. And those who didn’t had no appreciable change.
THAT would be a Eucharistic miracle.
I’m not claiming that current Eucharistic miracles serve no purpose at all. They do for those who already believe, and some who are caught up in the investigation, may also accept them.
But you have to understand, to a atheist who does not believe in a god, does not believe in a Fall of Man and Original Sin, and does not hold that Jesus Christ is the Son of God, it makes no sense to even need a Eucharist to begin with.
So, therefore the hype about these kinds of miracles is more likely to be regarded by atheists as polite, but nonplussed, disinterest.