HPE ProLiant DL380 Gen11 User Manual page 109

5. Attach the heatsink to the processor carrier:
a. Align the pin 1 indicator on the processor carrier with that on the heatsink.
b. Lower the heatsink on the processor carrier until the carrier tabs snap into place.
There will be an audible click to indicate that the heatsink is properly latched on the processor carrier.
HPE ProLiant DL380 Gen11 Server User Guide 109