it's a reverse threaded tool, it looks kind of like a tapered twist drill but without a cutting edge. It's usually used to remove broken bolts after drilling the centers. They come in a lot of different sizes. Since the screw you need to remove is small, you won't be drilling it out, just turn the easy out into the Allen recess (turning counterclockwise) with your fingers until it's snug, then use a tap wrrench to turn it out, also counterclockwise. The screw should back out with it. If it slips, try the next size larger. Be careful not to snap off the easy-out.