Singer Quantumlock 14T957DC Detailed Threading Manual page 23

Slip the thread into the center slot and then up and over the take-up lever slot.
Slip the thread into the center slot next to the take-up lever, then into the center
slot in the guides just above the needle clamp. Next slip the thread in front of
the metal guide and then into the eye of the needle in (D) position, through the
opening in the foot and then pull the thread tail to the back of the serger.