The missing piece is not really missing! It’s still stuck to the cable end.
[image|2266321]
When you lifted the cable off you snagged it pulling it off with the cable. If you look carefully you'll see a metal band with two little tabs this is the ring part that was soldered to the logic board like the one that's still present.
[image|2266322]
Carefully pull it off the cable connector if you have the ability to do micro soldering. You only have one chance to reattach the ring. If you don’t have the skills leave it alone! Get your system to someone who has the skills.