How do I replace the presser foot It fell off while I was serving

Hi Lois
Since "the wire" is still on the serger, it is most likely that only the foot came off, not the shank along with the foot. That is good.

The foot has a flat side, this is the side that comes in contact with the fabric. The other side, the one with all the bumps, faces up or towards the sewer when installed. The front of the foot is curved up, something like the front end of a boat. The back end has a bump of metal with a 'rod' (size of a pencil led) across it.

Hold the foot right side up by the front end. Slide it sideways under "the wire" (with the presser foot lifter in the upmost position) and now slide the 'pencil led like' bar under the shank. The shank has a claw like shape into which the 'pencil led like' bar fits. Now lower the presser foot so the shank claw fits over the bar ... it should click into place. If does not 'want' to click into place, press the small button/lever on the shank to open the claw for gripping the bar.

Please let me know how it goes.

Do a search (I use google) online and order one