It didn't happen.
God didn't kill the Egyptian firstborn or drown Pharaoh's army in the sea. He didn't drown people in a world-wide flood or smash them with burning stones at Sodom and Gomorrah. And he didn't kill Onan for spilling his seed or turn Lot's wife into a pillar of salt. None of this stuff happened.
These are all just stupid stories that no one should take seriously. The God of the Bible didn't kill anyone, because the God of the Bible doesn't exist.
But since half of the world still believes in him, I'll keep counting the number of people believers believe that he killed.
So let's pretend that the Bible is true and try taking the Exodus seriously.
Imagine Moses organizing the Exodus. He rounds up all the people (with their animals, baked goods, and silver, gold, and clothes that they stole from the Egyptians) and gets them all lined up and ready to go. Each family follows the next with a meter or so between them.
The Bible tells us that 600,000 men left Egypt in the Exodus, so there must have been about that many families. If each family was one meter apart, the line would be 600 kilometers long. That's longer than the entire Exodus route from the the Nile delta to Israel, even allowing for a bit of wandering around in the wilderness. So the front of the line would have arrived in Israel before the those at the end left Egypt. Yet the Bible says the trip took 40 years (everything takes 40 years in the Bible).
OK. So let's say it took 40 years. How fast were they walking? If the entire trip was 600 kilometers, then they would have had to walk a bit more than 1 kilometer per month (about 40 meters a day).
Of course there's no evidence that any of this happened. And if several million people were roaming around for 40 years in the Sinai desert, they would have left some evidence. But they didn't.
That's because it didn't happen.