it's most likely a dust on the focusing screen, u can try to clean it with the correct tool(plastic tweezer + a good blower or water flow from ur faucet) and a bit of youtube help(they hv a lot of video on how to remove & clean the focusing screen) or just go to Nsc for cleaning, either way it won't effect the image u take(if it's really on the focusing screen only), cheers
i think its really hard to clean a focusing screen - they're very fragile! if it really annoys you, then you should go to NSC. otherwise, leaving it alone would probably be the best option and if you look into most people's cameras you'll see quite a few spots too so no worries at all
(btw this dust isnt the normal kind of dust you'll find on shelves etc, it's actually metal dust that is produced from the lens mount scraping against the camera mount when you attach/detach it, and in Singapore because it's so humid, the dust actually gets damp (welded dust) and sticks better so it's harder to remove)
Not every lens switch will cause dust on focusing screen / viewfinder. And cleaning your dust is not a warranty service. If they do it for free than it's a gift, nothing that you can claim.
Learn to live with it. Be more concerned about your images instead of such irrelevant cosmetic details. Since it's on the focusing screen it will not show up in your images. Pay attention to dust on sensor, that's worth looking for.
It can't be on the sensor if you see the "dot" though the viewfinder; what you can see through the viewfinder is via the prism reflected by the mirror through the lens. You don't "see" anything as yet on the sensor at this instance.
After the mirror flipped, shutter open then the sensor gets exposed of the image you shoot. However you can't anything through the viewfinder at this instance. If the picture is dot less,at least to the naked eyes, then your sensor is clean.