It's not too bad, but it takes patience. Determine the desired length of the pull cord. You normally do this by placing as much of the old rope together as you can and then measuring it. Obtain the proper diameter line from your dealer, or a big box store. Put a knot in one end of the pull cord, and make sure that the other end isn't fuzzy, as you will be threading that end through the reel and shroud hole. An easy way to prep the line is to light the end with a lighter until it melts, then touch it to something and then pull it away slowly. This will leave you a fused end with a taper on it. Remove the shroud. With the shroud off, wind the reel tight. While holding the reel under tension with one hand, thread the tapered end of the line through the reel and out the hole of the shroud. Pull the line all the way through, and seat the knot. Place a knot about 6" from the end on the tapered end that you passed backwards through the shroud. If your pull cord passes through an eyelet on the handle, away from the shroud, thread the line through this before tying the knot. Slowly, release the pressure that you've been holding on the reel, and allow the reel to feed in the pull cord. The knot will not allow your line to be retracted fully into the shroud. Install the handle, and untie the knot in the line. Reinstall the shroud onto the machine.
Hope that this was helpful. You may rate this solution, if you like.
Best regards, --W/D--