SINGER 14T967DC-WORKBOOK QUANTUMLOCK - Manual (Page 53)

Install the Knife Cover.
Engage Upper Looper. Engaging the Upper Looper causes the looper move when
sewing. Even though the Upper Looper is not threaded it needs to be engaged.
1. Push the clutch button to the left and down to engage.
2. Turn handwheel.
Upper Looper Disengaged
Upper Looper Engaged
Three-Thread Overlock (narrow) page 6