Dell OptiPlex All-in-One Plus 7410 Owner's Manual page 81

Steps
1. Place the power-supply fan on the display-assembly base.
2. Align the screw holes on the power-supply fan with the screw holes on the display-assembly base.
3. Replace the two screws (M3x5) that secure the power-supply fan to the display-assembly base.
Removing and installing Field Replaceable Units (FRUs) 81