Lenovo THINKCENTRE 6019 - Manual (Page 126)

5. Position the replacement memory module over the memory connector. Make
sure that the notch 1 on the memory module aligns correctly with the
connector key 2 on the system board. Push the memory module straight
down into the memory connector until the retaining clips close.
6. Go to “Completing the parts replacement” on page 148.
120 Hardware Maintenance Manual