Instructions
Press the "Tilde" key ("~"), located next to the "1" key on your keyboard, to access the in-game console.
Type the following phrase to bind your mouse scroll wheel down, where "action" is the associated action that occurs when the scroll wheel is scrolled down:
bind "MWHEELDOWN" "action"
Type the following phrase to bind your mouse scroll wheel up, where "action" is the associated action that occurs when the scroll wheel is scrolled up:
bind "MWHEELUP" "action"
Type the following phrase to bind your mouse scroll wheel when it is pressed in, where "action" is the associated action that occurs when the scroll wheel is pressed in:
bind "MOUSE3" "action"
Press "Enter" after the command has been typed to bind that key to the action.
Use your mouse scroll wheel in-game to perform the action you have selected.