My water well caved in, how can I fix it

Drill a new well.

Is this a bored well or a drilled well?

Or a dug well, my older "sharecropers" house in south Georgia, now used for hunting, had a well that was just dug. (South Georgia can have very shallow wells)
It was dug by hand.

But in general, you will have to get the well company to come out and fix it, not much you can do on your own.