After you have a small break in the flange, grab one end of the flange with a good pliers and pull in a radial direction. Because of the score line in the Speedi-Sleeve next to the flange, the flange will tear right off and leave a clean edge on the remaining sleeve. This process reminds me of using a key to wind and tear the narrow steel strip from the side of a can of sardines or coffee. That simple design predates the age of pull top containers, so some of the younger among us may not remember the pleasure.