These should be the green blobs which drop when you kill enemies, when you press E while near them it opens up bodypart menu with the bodypart in the stash. After that just drag and drop it into the correct slot and boom, stats increase.
Adding it into comments, I made the cloud into dash controls a bit smoother and added Linux and Windows downloads. Web version is a bit bugged by visuals and smoothness, so if possible try to use the downloads.