I was able to screw the roller fixture back into place, however, the right side now rides high:
Many thanks to Trevor's helpful response. Given isherwood's feedback I will attempt a more specific follow-up question: Should the right-side gap be corrected \ closed by tightening the tension on the left or reducing tension on the right? Any explanation of why is appreciated.
In an attempt to replace the (bottom) roller of the garage door, I did not notice that it was tied to a cable and now it is difficult (if not seemingly impossible) to restore because of the cable length seems short. The reason for replacing the roller is that was exposed to saltwater flooding and it may be the causing the door to stop after moving 2 inches (from either the open or closed position).
Is there a good explanation and video that can explain the purpose and mechanism so that I can safely restore the garage door back to working order? If I can learn how the mechanism works from a good-simple youTube video or URL, then I can troubleshoot the other umpteen garage doors in the community. Thank you for an lessons-learned and pitfalls to avoid.