You may find people "successfully" removing the white stain or fungus marks by nail polish remover, thinner, or even lighter fluid. However, those are the organic solvent. They dissolve a thin layer of the rubber from the surface. The whitened area is eroded and removed.
The organic solvent actually etches away part of the rubber. It may create micropores on the surface of the rubber and make it more prone to the coming oxidation.
People will find their lens rubber whitens even faster later and sometimes cracks will appear on the rubber.
Your precious lenses deserves a delicate lens rubber cleaner than can rejuvenate and protect the surface from further oxidation.