Oh, the rage. (nation red)

Bought the game, installed and when i entered it, i accidentally changed the "move forward" control, with the "LMB"...and i can't change it no more. It says that i should press enter to change it, but it won't work. Does anyone know what to do?

Later edit: looks like the game was trollin' me or something. Now works fine. Just a few curses and it works like a charm.