I may not be clear on what you are having issue with. I haven't ordered a "new" 2xxx chipset mobo yet....but...
Both of the AM4 mobo I have ordered so far by default use a backplate and screws to mount the cooler. Both of the mobo came with what I presume was a previous version of system with two plastic blocks with lugs to clamp to. I had to remove those from the mobo to install the "stock" AM4 cooler to both.
Are you missing those blocks?