So my brother recently bought a Canon M50 mark ii and I don't remember how, but I accidentally touched the viewfinder with my finger/thumb as he found a fingerprint smudge on viewfinder the next day. He tried to clean it with his kit, but he said, now it cannot be cleaned and that smudge has caused some kind of "discolouration" and now his viewfinder will not give accurate colours. He said now it will need professional cleaning or even replacement! and it will cost a lot as they would need to dissemble the whole camera and this will not be covered by warranty! I don't know anything about cameras and it was the first time I held an expensive one. I feel bad because he blames me for not knowing how to handle cameras, but I also think it is dumb of the company to keep such a delicate part vulnerable to touch and will not give any kind of protection. If you know about cameras, please tell me if I really messed up his expensive camera or can this be fixed without spending a lot of money.
give him a slap and tell him to stop taking the piss. i have cleaned my M50 view finder without any problems a few times i use the alcohol free glasses cleaning fluid from specsavers, i've had mud, and clay on it too and its cleaned off fine. canon and any other camera company know the lenses, view finder and sensor are going to get dirty, be touched and cleaned in un appropriate ways from time to time, they have built in some general resistance to this sort of thing. even the sensor is pretty resilient as its behind a filter ot two and a cover glass the most delicate part of the camera is the actual shutter blades, they get touched and its a different story, one tiny warp from them and its game over thats why you never use cannned air to blow off the sensor, just use a hand rocket pump / blower or a sensor cleaning kit (in a year and a half i haven't needed to clean my sensor yet)
Welcome to the forum, Mihir, If it is only the view finder and nothing else, this will clean up with a eye glass cleaner and a soft cloth, Now I suggest you don't touch his stuff as sibling rivalry can leave to discontent within the family and if all else fails run to mum and dob on him for upsetting you.
Mihir, do not worry you did not ruin the camera, your brother is way over-reacting. Caladina already advised that glasses cleaner will get the oil from your fingers off the glass in the viewfinder. These cameras are not cheap and are made to be durable. It sounds like he wanted to scare you away from touching it again.
Your brother seems to be ruining your childhood with such unfair means of guilt. But not to worry, it may look like a tough job to clean the viewfinder but now the manufacturing company gives an automatic version of the same which is a built-in feature in your Canon EOS Mark II. Refer here, how-to DIY using the camera settings.