In this game, you can't. It's using a newer version of Unity which has customizable keybindings disabled by default.
For what it's worth, most Unity game developers agree it's dumb. There's a thread on the Unity forums full of people complaining, with the Unity developers telling us that we don't actually need it, and that we should suck it up and program our own custom keybinding UI for every single game we make.
Gah.