Well you could do a few different things. Like taking a toothpick and dab a little superglue on it, then stick is into the hole with the screw. Wait a few mins and then try to turn it while pressing the case down. If you can't manage to tighten it then get a pair of plyers and try that with the pick. If it works just try to take the pick out, but if you can't then break it off with a little stickin in the hole.
Or
You could by the torx 6, for like 3-4 dollars
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