That's some old-school stuff there. They taught us about that procedure when I was in vet school... 40 years ago... but they didn't demonstrate it, and I never saw or heard of anyone who actually did it.
Essentially, it's a plastic 'nail', with a button that fits over the 'head', then you shove it from inside-out, through vaginal wall, pelvic musulature, skin, and slip another button over the pointy end, slide a cotter pin into holes pre-drilled in the shaft, to hold it in place. Rinse & repeat on the other side.
https://www.outbackvetsupply.com/product.jhtm?id=713&cid=183
Working on mostly Beefmasters & Gerts when I was in practice...30 years ago... I saw plenty of vaginal/cervical prolapses. Just did an epidural, cleaned 'em up, shoved 'em back in, and did a Buhner stitch - and recommended pounding them out... but, since so many were 'valuable registered' cows... not enough of them went to town. Most calved relatively uneventfully, even if the owners didn't follow my instructions to keep them up and cut out the stitch when calving was eminent. Guess the cotton umbilical tape we used had rotted enough by the time that most got around to calving that it just broke (or tore through... IDK).