Lenovo ThinkStation PX Manual page 9

Onboard M.2 SSD drive installation
1. Open the side cover on the PX and remove any PCIe adapters that may
interfere with accessing the onboard M.2 slots.
2. Rotate the red locking mechanism counterclockwise.
3. Slightly lift straight up to about a 15-degree angle and pull out.
Caution: Be careful not to lift too much to risk breaking the M.2 slot.
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