First there is genetic transfer from cell to cell. This is still extant, not some ‘missing link’. Then there is hermaphroditic exchange of genetic material during reproduction among multicellular life forms - once again extant and not at all “missing”.
So there was no need for males and females to develop simultaneously and in isolation, amazing that you have never heard of hermaphrodites.
Did you know that in utero we are still hermaphrodites? That based upon hormone levels one set of genitalia develops (usually) and the other is reabsorbed?
This is a typical creationist fallacy - sort of like asking how the new member of a species could find a mate.
That is as idiotic as asking how the first speaker of Italian born from parents that spoke Latin found someone to talk to.
Do you need me to explain why to you, again?
How is it that everyone else thinks a person’s sex is determined by either the X or Y chromosome from the man?