Looks like it could be a case of infected single eye popeye (normal popeye shows white tissue popping out). Being a single eye, the cause is more likely to be an injury from hitting something sharp in the tank, or being attacked by a tankmate.
If it is popeye, one option is to isolate the the fish and gradually build up the concentration of Epsom Salt over a number of days, which will draw water out of the fish and help the swelling stop increasing in size (and in time help healing). Combined with a general anti-bacterial medication like Esha 2000 or Myxazin, this should hopefully clear up any infection and then the tissue should start to repair itself over a number of days.
I'm not confident with giving specific dosing specifics of the above, I've only ever used Epsom Salts with Persian Killifish, which are very tolerant of water chemistry changes (so if I recalled rightly, I increased the concentration by 1mg/l per day for three days). I would imagine that 0.5mg/l per day until ~3mg/l is reached would be very safe with Kribs, but this is not something I could guarantee. Don't forget to gradually reduce the concentration of Epsom Salts after the fish is fully recovered, again over a number of days.