Alux

Probably a stupid question but I brought the LINKUP - Ultra PCIe 4.0 X16 Riser Cable from eBay. Not sure if its just supposed to come with the cable or what. But it's my first time trying to install a vertical mount (had it on my H1 but the riser was pre-installed) and I'm having issues installing it. I see theres a big circular opening in the front and a smaller one in the back. Is there a particular screw I'm supposed to use or something or