I need to find a dress for a special occasion and it's suppose to be easy to find a dress, but in my case I have a scar on my upper shoulder arm. Can someone have advice with what kind of a dress I can find, such as brands to cover up this scar of mine. :D

Depending on the weather, you could wear a cute sparkly sweater over a less ornate dress.
Since I don't know where on your shoulder the scar is or what size it is, I don't know much more to say. Perhaps sheer sleeves. Check out different strap sizes, perhaps short sleeves
Or 3/4 length sleeves.

Find some make up your skin tone and cover it up.

If it really bothers you then you could try to cover it up w/ makeup. If that doesn't work or you don't want to do that then maybe you could look for an off the shoulder dress. I'm not exactly sure if that's where you're scar is but if its around the area that the straps would fall, then you could try it. Hope that helped :)