Dell Latitude 3390 2-in-1 Owner's Manual page 26

Installing the Input-Output board
1 Place the I/O board on the laptop.
2 Tighten the screws to secure the I/O board to the laptop.
3 Connect the coin cell battery and power and volume button board cables to the connector on the I/O board.
4 Connect the I/O board cable to the connector on the system board.
5 Affix the adhesive tape to secure the I/O board cable and release the copper latch.
6 Install the:
a battery
b base cover
7 Follow the procedure in
26 Removing and installing components
After working inside your computer.