Unless you are among the Gifted Few, KappaRaider, the answer is...
Swivel first consciously according to the Instruction given in The Golfing Machine and in these pages.
Then, let the motion happen subconsciously.
Watch (in The Gallery) the 6bmike video short "Ready To Roll On the Plane" and duplicate my rotational Wrist Motion with a dowel in the FIST of your Left Hand -- NOT a regular Golf Grip.
If you don't KNOW that you are Swiveling...
Assume that you are not.
Because you probably aren't.
Here is a great view of the Finish Swivel of PGA TOUR player Arjun Atwal as he lets loose on his way to a 64 in yesterday's first round of the U.S. Bank Championship in Milwaukee. Note that the Left Wrist has remained Flat and that the back of the Left Hand and the palm of the Right Hand have Snap-Rolled out of the Follow-Through (the Both Arms Straight position) and into their 'parallel to the Plane' conditions for the Finish (2-G and 4-D-0).