How can I turn off the tutorial?

I don't think you can. I did the same thing (on accident)
I clicked it thinking at first it was the game guide.
You just have to let it run through and keep clicking "ok" until it is done.
It will say "replay tutorial instruction" across the top of the screen until one of your villagers has a baby.
At that point, it will finally go away!

It can be stopped by completing it. Or, if you'd rather, you can start a new game (and new tribe) and select 'no' for Do you want help at the beginning.