Mac Pro (2019) SSD Adapter Installation Guide
If installing a second drive, install two small brackets onto the top side of the primary drive, crossing over the main bracket
Attach your secondary drive to the small brackets, facing the same direction as the primary drive
Assembly is complete. Now onto installation!
Unplug all cables from your Mac and remove the cover, following Apple’s instructions
Connect the power and data cable(s) to the motherboard connectors located above the PCIe slots)
Sandwich the adapter into the slot using the original bracket — being careful not to overtighten