Canon EOS M50 Mark II Advanced User's Manual page 56

2.
Attach the lens to the adapter.
Align the red or white mount index on the lens with the corresponding
mount index on the adapter and turn the lens as shown by the arrow
until it clicks into place.
3.
Attach the adapter to the camera.
Align the white mount indexes (3) on the adapter and camera and turn
the lens as shown until it clicks into place.
(1) Red index
(2) White index
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