Fruit Tea- Tastes Sour?
Your question seems to assume that the sour flavor is not how it's supposed to be. But that may simply be how the tea you've bought always tastes. If it's really sour, maybe it's just not a good tea; it could also be that you simply don't prefer this kind of tea. You could try to cover it up with a bit of sugar. But failing that, I think this is just not the tea for you. There are tons and tons of fruit-flavored teas out there, so I'm sure you can find some different ones to try.