I have never known a hernia belt work for anything other than giving a foal sores!
It is only a minor hernia and any vet in the know would ring it.
This is using a rubber ring that is used for docking lambs tails. The hernia is first pushed up, then the skin is ringed tightening it right up holding the hernia up so the muscle can grow over the gap.
After a couple of weeks the skin sloughs off.
I had two brood mares whose foals nearly always had umbilicus hernias. I tried hernia belts but they never worked - ringing did.