Open the config.ini, found in the games main folder.
Look for the line called Key_Def
These values are your keybinds.

you can replace the entire line with this one

Key_Def = [forward] 00 [backward] 00 [left] 00 [right] 00 [change target] 00 00 00 [aim] 00 00 00 00 00 [run] 00 [fire] 00 00 00 [options] 00 [status] 00

then replace the brackets with the key you want.
Microsoft has a page I cannot post a link to, but it should be the top result of every search engine.
ignore the 0x before every value. We just want the last 2


Yours should look like this

Key_Def = 57 00 53 00 41 00 44 00 45 00 00 00 02 00 00 00 00 00 10 00 01 00 00 00 1B 00 09 00

Don't leave any brackets, and ignore the 0x before every value.

Key_Def = [up] [up2] [down] [down2] [left] [left2] [right] [right2] [changeenemy] [changeenemy2] 00 00 [aim] [aim2] 00 00 00 00 [run] [run2] [fire] [fire2] 00 00 00 00 [status] [status2]

Tested the rest of the values. They're all backup bindings. Nice for having shoot/interact on two buttons.

The last blank value opens the in-game keybinder which is redundant so I'd leave it blank.
The other blank values don't do anything. They're leftovers from the PS1 version. 6 blank values for 6 blank PS1 buttons.
(5 in Directors cut)