Janice,
This is a relatively simple procedure. In the manual that accompanied your mower, there should be an exploded diagram that will show you where the pull cord mounts. Simply remove the 3-4 screws that retain the cover and the pull rope pulley will be evident. You can buy a replacement pull rope at Sears and just make sure you wind it in the direction as indicated on the instructions. Remount the cover and voila, you're good as new. Hope this helped.
F. Graves, July 2006