I'd be a bit cautious about doing any thing. From the photo and your description I think there is a good chance you are dealing with an inguinal hernia. Last thing you want to do is put a band around a loop of intestine. I think you should get a Vet to check it out before doing anything.
I have banded a lot of calves. I have seen a few that I could not find the 2nd nut. I have never put a band on one nut. A lot of times you can wait a few weeks and the 2nd nut will come down. I would wait and see what happens to this calve but watch for infection and get vet to look before doing anything.
