When opening the ‘Preview’ window, we show the entire job process, advanced to completion. We also provide a way to scrub or slide through, from start to end, with the ‘Play’ button and a slide bar (
) for “scrubbing” back and forth through the process.
The slider can not be all the way right, showing the completed job, for the ‘Start here’ to become available. You can’t “start” from the end. 
Scrub back away from the end to the exact place you want to Start, and you should see that button available. Click to open the options.
