How do I reattach a SubZero refrigerator door handle?
There should be a small set screw on the inside of the handle (opposite side of the picture). This is usually driven with a small Allen key.  Loosen the screw, place the handle back on flush against the door surface, and tighten the screw finger-tight. Don't over tighten as they strip easily because they are so small.

The screw will look something like this


(source: funrcboats.com)  

There might be a small plastic cap over the set screw in order to better hide it.