Hiya, If the steering box is still on the vehicle then just start the engine and shake the steering wheel.
Make sure you put a drain tray under to catch the mess. If you have removed the box then the easiest way i have found is to drill two small holes through the washer and seal then screw in a couple of long self tapping screws.Once the screws have passed through the washer and seal they will bottom out and push the seal out.
Good luck.