Did you lose those tiny screws in the carpet?
You can find a replacement in this set... unless the missing screw was holding the heat sink on... then you're sunk.
This set includes all the screws except those from the logic board heat sink. The heat sink and it's screws are included with the logic board.
- MacBook 12" Retina (Early 2015)
Lifetime Warranty - This iFixit product is guaranteed to function as long as you have it.