When I need to repair zig zag, I take out the bad spot and take out about 1-1/2 inches on each side leaving the thread tails. I then pull the threads to the same side, knot and using my easy thread needle, bury the threads. I then hand turn the machine to position the zig at the right spot and zig zag the error spot in. I then pull my thread ends to one side, knot and using my easy thread needle, again bury the ends. I can usually get a virtually invisible fix.