It's a plate to mount your chain guard to, the only way to remove or replace those is if you remove the entire crank bearing because it is mounted though that to keep it in place.

• First you'll need to remove the cranks, pop the plastic cover, and use a 14 mm socket to remove the bolt, you can either use a dead-blow carefully or use a bicycle crank puller if you have one (this is easier).
• You'll need a specialized tool to remove the cups, however looking at the retaining ring on the other side it looks like this one is metal. If you have a blunt chisel and a hammer you can try and use that. But be careful, you do not want to damage the threads in the bike, if you do that there is no way to fix them and you can throw it away.
• After removing the entire bearing hub is out, the chain guard mounting place can be removed and you can reassemble the bike again if you are not replacing it with a new one.
• I don't know for sure anymore but it can be that the fasteners are all tightening towards the front, meaning one will tighten clockwise and the other side counter clockwise.

This is based on my previous experience working in a bicycle repair shop.