This is a common question that creationists come up within their typical "grasping at straws" tactic in trying to explain such an untenable belief.
The fact is that an informed atheist would never make an assertion such as "something comes from nothing" in the first place.
Quite simply, Nobody knows how "something" came to be or whether the universe physically exists.
But this is where creationists are only too willing to make an assertion from an assumption, i.e. that something comes from something.
Then, to take it a step further and make another assumption, "That something must be a creator."
Then, Of course, Out come the usual bizarre stories: "The creator is invisible and elusive for, er, um some reason, he is everywhere and, oh yeah buster, you better believe what I say or else the creator is going to keep you alive after you die and punish you. . . . and like, forever. . . . . so there, I'm right. . . ok, Like I'm right, and that's a fact."
So, What gives creationists the right to make "something" up?
And by their own reasoning, if something must come from something, where the heck do they think that that second "something" come from?