Dell NOT21990 Owner's Manual page 112

Steps
1. Align the ports on the system board to the port openings on the palm-rest and keyboard assembly.
2. At an angle, carefully slide and place the system board on the palm-rest and keyboard assembly.
3. Align the screw holes on the system board with the screw holes on the palm-rest and keyboard assembly.
4. Replace the screw (M2x2) and the four screws (M2x3.5) to secure the system board to the palm-rest and keyboard
assembly.
5. Connect the following cables to the system board:
a. I/O daughter-board FFC
b. eDP cable
c. Power-adapter port cable
d. Keyboard FFC
e. Keyboard-backlight FPC
NOTE: This step applies only to computers shipped with a keyboard backlight installed.
Removing and installing Field Replaceable Units (FRUs) 111