Jewelry - ring sizing

We have a ring we’re giving to my mother-in-law. It’s a size too big, and I seem to remember my grandmother had a . . . like a bar, sort of, on the underside of the back of a ring she owned, to make it fit, as opposed to tradition resizing.

Is that a thing? How does it stay on? Is this a DIY or a jeweler thing?

Jeweler thing. $5-10.

Ring adjuster.
Different kinds Google