One of my fingers is curling inwards after an injury.
I have a wooden roller that I apply vigorously to the palm a couple of times a day to break down the scar tissue, should be more often but.... and I keep straightening the finger under hot water, and when I'm sitting reading of an evening I straighten it, and I wear a splint in bed to keep it straight.
It's two months since the injury and I expect to be doing this for several months more.
That said, it's just bent, not bent all the way to the palm as can be the case with Dupruyten's , but I think one has keep at it. Scar tissue builds 24/7.