By the looks of it the 0 key should open a settings menu where you can set the keybindings.
Alternatively you could use the console to change the key, type this into it:
Set "Global name" to "Key number"
Replace Global name with one of these:
- Global list:
And replace Key number with the DirectX Scancode of your choice, for example G is 34.
So to change the long reach key to G it would be:
Set GroovyReachKey to 34
Hope this helps.