Hi and welcome to the forum
Can you post pictures of both sides of the fish so we can see both of its eyes, and a picture from the front if possible so we can see if the white bits extend out of the eye?
How big is the fish?
Is the fish eating now?
If yes, does it find food easily or does it swim around missing everything?
Maybe post a 1-2 minute video of the fish eating and swimming around with the others. You can upload videos to YouTube, then copy & paste the link here.
What does the fish's poop look like?
It could be the start of cataracts but they don't normally occur on young fish and normally the black part of the eye goes completely cream/ white.
It looks like the white bit is excess mucous on the eye and that could be caused by physical damage. However, a picture showing the fish from the front and other side would provide more information.
It looks like a young male and it might have been bashed by other fish before you got it and damaged its eyes. It might also have some mental health issues (stress, ptsd) if it was attacked and badly injured.
The fish has some excess mucous (cream bit along the edge) and a little bit of damage on the upper half of the tail. This is normally caused by poor water quality or a dirty tank, substrate or filter. If the fish is sick or in a weakened state, it will be more likely to have issues like this compared to healthy fish in the tank.
I would increase the size of the water changes to at least 50% (preferably 75%) and do them a couple of times a week or even every day for a couple of weeks. This will dilute any disease organisms in the water and give the fish a better chance of recovery. After that I would do a 50-75% water change once a week or once every 2 weeks (preferably weekly but it depends on if you can).
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.
Make sure you gravel clean the substrate whenever you do a water change.
Established filters should be cleaned at least once a month, so clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use the media. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens, which should help the fish overall.
If the fish is blind, try not to change anything in the tank. It is the same as a blind animal or human, you don't move stuff around in their home because they walk into it. Try to keep everything in the same place in the aquarium.
If the fish can't find food, then you might have to hand feed it. This can be done by holding frozen fish food with your fingers and wiggling it near the fish or at the surface. Or you can use a pair of round nose tweezers to hold the food. Use round nose tweezers rather than square or pointy end tweezers so you don't injure the fish if it bites them. Try to feed the fish at the same time and in the same place each day.