Thanks, @fishyculture! That's cool you're gonna give it a try. There are a ton of videos on YouTube about it. This was the first one I watched:

I followed her instructions, and have had a lasting difference. But I think it's because the furrow and crinkling is not the glabella's natural state. Flat is its natural state. And being flattened really does seem to help the muscles remember/retrain themselves to stay at-ease, and not tense and tighten. The massaging helps that retraining, too.

And, maybe most importantly of all, is to pay attention to your facial reactions. Had I not watched that video I made for @jerrybanfield, I wouldn't have seen how severely I squinched! Hope you have pleasing results. :-)