The clasp slides into channel and slips inside button replacement tool (Image 1). Make sure the string is sitting in a little bump on the clasp. Keep tension on the string while pushing the tip of the replacement tool through the hole where the button fell off. Hold strings with one hand, push the plunger (Image 2) of the tool to release the clasp, and then twist and pull out the replacement tool.
String the button on and make an overhand knot with two ends. Tighten until the button is the same depth as the other buttons. Make another overhand knot to hold the button in place. A third knot goes below the button to lock it. Snip off strings and tuck ends behind button.
Gather tools (in this case, the curved upholstery needle, heavy-duty nylon and scissors). Cut about 1' of heavy-duty nylon thread. Tie four to five overhand knots in one end.
Thread the curved upholstery needle, insert the needle just beyond and into the tear, go back through top of fabric, pull tight, go back behind thread, loop through bottom fabric and pull tight. Repeat the process and pull tight at end, making several slip knots to bind -- loop needle behind last stitch and into middle of fabric and snip off flush.