Last four pairs: pair two
Step 1 / 7
Dw: 2 Bottom layers: turn 90°, front face goes right
Eight pairs are done. The two pieces to pair are on the two front edges, same color on the front.
It pairs two edges at once and keeps finished pairs and centers intact.
Step 1 of 7: Dw. 2 Bottom layers: turn 90°, front face goes right