Stains/discoloration of natural stone pavers

hi there. I have a flagstone patio made from a stone called “bronte.” I think that is a sandstone but not 100% sure. Never been sealed

anyway, part of the patio never gets any sun and so had accumulated some mildew and so I used a cleaner rated for natural stone and I guess I left it on too long because one (and only one) paver got bleached out. Picture attached

wondering what the best way is to combat that bleached out look. Hoping not to have to replace the paver

can I use a concrete grinding cup on and angle grinder or something else and maybe mechanically sand off enough surface to get down to undamaged stone? Just worried about swirls and scratching that could look just as bad. Maybe a poultice and just good old elbow grease?

Any advice appreciated !