Is there a way to 'de-stretch' a crocheted piece of clothing?

I have a hat that’s special to me. It’s the last thing my mother made for me before she died, over 25 years ago. Objectively it’s nothing special. It’s pretty much a round disk, mostly of double crochet stitches that grows out from the center until it’s several inches larger than the biggest diameter of my head. Then it reverses and starts to get smaller again until it’s basically the size of my head – so these two parts will just lie flat together like a pancake if set on a table. Then there’s a band, about an inch and a half that forms a right angle to the rest, which is what fits around my head to keep the hat in place. Basically, when worn it looks sort of like a slouchy, over-sized beret.

The problem is, the band part has slowly stretched out over the years, to the point that even the slightest breeze is enough to make the beret lift up and blow completely off my head.

So what I want to do is tighten the band back up to what it used to be. Because it’s attached to the not-stretched out beret, I can’t just take a tuck or cut out a section. I think it might be possible to take more yarn and sort of do some stitches around the inside of the band, basically making mini-tucks in each crocheted stitch to draw it back in without changing the look of the hat.

But maybe there’s an easier way to restore the original size of the stitches? Or is it that the yarn itself stretched, and I need a way to make it contract again?

Anybody have any knowledge about this?

BTW, in case it matters, the entire thing was crocheted as a single item, just with increasing and decreasing numbers of stitches. It an off-white acrylic yarn, I believe.

Do you ever wash it and dry it in a dryer? I have some hair elastics that tighten up like new when I do that.

If the yarn has lost it’s stretch/release, there’s no way to restore. Entropy.
Don’t try any shrink treatment. All that will shrink is the other un-stretched yarn.

You need to either add more yarn, or similar material interwoven or some elastic.

The alternative is to unpick and then re-crochet the garment. But at best this will add some stretch based on the weave which will decay at some stage, likely quickly and it will never really look like the original.