My wife ran over our trash can which was unharmed except that the wheels popped off.
I needed to pop the axle back into the slots. I gave it a go but it was too hard. I tried again, and again. I pried the slot open with a screwdriver, and pushed down really, really hard. Pop. Trash can fixed.
Don't give up. If things aren't coming together, remember there's usually one easy way to fix things and a lot of hard ways to fix things. You just have to find out what the easy way is.