The documentation is here, https://docs.unrealengine.com/5.0/en-US/optimizing-rendering-with-pso-caches-in-unreal-engine/
I am doing this at the moment for my game and have successfully collected the caches while playing the game. I am stuck at the point where I have to covert the PSO cache also know as expansion using a cmd commandlet. If you do get to this point please tell me how it works.