Lost access to drawer icon for center button on CyanogenMod 7

I am running CyanogenMod 7 on my HTC Thunderbolt and somehow I inadvertently removed the function for the center button on my home screen between the phone and web browser icons. This middle button used to bring me to the drawer where every installed application is listed, not just the ones on my home screen. How can I restore the middle button functionality to get access to applications in my drawer?