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This should pierce the plastic and pull it up.  You'll be able to see the metal plate below it.  The pin should easily slide through the now-free hole and the tag should be removed.
Place the item of clothing on the floor with the ink cartridge facing up. Take a very thin flathead screwdriver and place it along the edge of the raised square pyramid. Press down hard. Continue to pop up the perimeter of the plastic. Remove the silver paper lining. Use the screwdriver to lift one of the metal arms that holds the pin in place. Slide the pin away from the tag.