i have a simplicity frontier sergers...this is what it says "sewing with the upper blade disengaged"
unblug the machine
open the front cover
turn the hand wheel towards you until the upper blade is at its lowest point
push the upper blade to the right as far as it will go and turn knob in opposite direction until it clicks into position
to re-engage, push blade holder to right and turn blade towards you until it clicks into position.
hope this helps!