This chip is known as an interposer. It’s essentially a bridge between the Mini Mono RAID controllers and the backplane. Without the interposer you are unable to install any of Dells mini RAID controllers. You can however install a regular PCIe card though. As I pointed out in this post, it limits you to a variation of riser 1 that has no x16 slot.
Installation instructions
Find the interposer slot located right in front of Riser 1. This is near the top right corner of the chassis. Match up the slot and press down until you hear the interposer snap into place.