HP ProBook 4321s Notebook-PC - Manual (Page 113)

4. Turn over the palm rest (1), resting it in the palm rest tray, and then slide the palm rest to the left
to reconnect it to the base enclosure (2).
5. Replace the screws in the palm rest.
6. Place the keyboard upside down on the palm rest of the computer (1).
Replacing the hard drive 101