a) suppose there are infinite multiverses, and in one of them a smart being learns how to communicate between multiverses. By building computers in all of them and collecting the computing power of infinite computers, this being becomes infinitely wise. This is equivalent to the word “God”, so the multiverse proves the existence of God.
b) It is irrational to think that multiverses only differ in their physics. They should also differ in their biology, their chemistry, and their mathematics. Since the math varies in each multiverse, let us suppose there is a multiverse in which actual infinities are logically impossible. Then it disproves the existence of a multiverse. Therefore there are no multiverses.
Egnor just sums it up and says it makes no sense. And he is entirely correct.
See also: Michael Egnor on why the multiverse is just a way of evading reality. Egnor: The fact that the universe is tuned — that is, the fact there is any consistency at all in the laws of physics — demonstrates God’s existence. This is Aquinas’ Fifth Way, which is the proof from design.