I used to work at a vet clinic and we got one or two a year. Fixing it can be done, if it's not too bad, and the calf gets to the clinic right away, but it really takes more than can be done at home. We used to anesthetize them, put them on their backs, prepped and cleaned up, make an incision, put everything back in, while making sure it was clean and sterile. (Which can be a big job if there's lots to deal with). Then the abdominal wall needs to be sutured, followed by a row of sutures in the skin.
Unless it's only a tiny wee bit sticking out, it's most likely to work if you take them to the vet. We saw some where literally feet of intestines were hanging out. It's pretty incredible sometimes. We had pretty good luck with the procedure, but even then it didn't always work. The bad ones were a high risk for shock.
That being said, calves are worth some money now, so checking the vet to see what it would cost wouldn't hurt..... As long as it hasn't been too long. Things deteriorate pretty quick when insides are out.