You will have received several bags of screws. I assume the screws labelled as 6-32 would be the ones for an additional case fan. If you don't have that screw then you can find some online with the same size of 6-32. Or if you have it and it doesn't fit? If that doesn't fit then get a longer one, but judge based on how short the 6-32 screw is. Your local hardware store should have a wide variety of screws so give that a look as well.