Keep trying and go to a VET if the situation worsens considerably. The wound must be kept open and draining for about a week. Each day, soak the turtle for awhile and then wipe the wound with a Q-tip, getting out as much of the matter as you can see. The cap of the Bic pen can also be used as a tool for pushing on the outside of the wound to try to push the matter to the surface. A sick box turtle should be placed in a large cardboard box with a heating pad set on low - underneath part of the box.
Box turtles are native to the east and mid-western states.
They are collected from the wild in massive numbers each year and shipped to wholesalers, pet shops, etc. Many are shipped overseas to England where their slow deaths are ensured. By the time you buy one, you can be sure that the box turtle has suffered severe stress from his ordeal.