SINGER 14T968DC - Manual (Page 70)

5. Turn the handwheel toward you until the lower looper extends 5-10mm
(approximately ½ inch) from the needle plate edge.
6. Thread the looper area of the machine following the green color coded
thread guides 4-9.
7. Thread the hole in the Upper Looper from front to back . Pull about 4
inches of thread through the looper and place to the back of the
throat plate.
Three-Thread Overlock (wide-decorative) page 4