It’s interesting what you’ll encounter as you move away from character modeling.
I wanted to straighten all the vertices diagonally. The most common way to go about doing this is “S” (for scale) and then Axis [X, Y or Z] and then “0.” But to achieve this diagonally, you need to reposition the Gizmos. After a bit of thinking, my approach is this: Set the Transformation orientation to “Normal.” And Transform Pivot Point to “Active Element.” Select all the edges that you want to straighten… make sure not to select the straight edge first. The edge that is straight should be the last to be selected, so that it becomes the active element, and all other edges will line up.
This will work out perfectly if your active element is actually “perfectly straight.” But what if it’s not? You can manually reposition it so that to the human eyes it looks straight, but you can’t be certain that it is.
Luckily, I had the outer ring untouched the whole time. I used that edge as the active element. And voila!
Just think ahead. Make a duplicate of an edge from the start and leave it there in case you might need to use it as an active element to straighten your vertices down the road. If you know of another way, I would love to hear it in the comment section.