I have a Nikon D3400. I took this picture by holding my smartphone up to my viewfinder. There's a small black dot in the lower right corner. It's still there if I switch lenses, however it does NOT appear in photos. I tried cleaning the outside of the viewfinder, but it didn't come off, so I'm guessing it's a piece of dust on the inside of the viewfinder.
What are my options for cleaning it? I guess since it doesn't show up in photos, it's not a super huge deal, but I'd rather it not be there.