It took longer to take the food off the shelf above the crisper drawers then it did to install the new center guide.
Once you remove the food, pull out both drawers, remove the glass shelf insert then lift out the shelf frame. Remove the broken center guide and replace with new one. No special means to replace it, just look how its setting in there. Then put all the frame, glass and drawers back in. Good time to through away that old food from yesteryear.