Starting at the end that will be inside the ring, use a small rubber/nylon hammer to shape the band end on a ring mandrel. It is best to start at least two sizes smaller than the finished size desired as the ring size expands during shaping. Continue wrapping the ring around the mandrel and shaping with the rubber/nylon hammer. Reverse the ring on the mandrel often during shaping to avoid a slight cone shape to the ring.
Pro Tip: If making wrap rings to give away or sell, do not patina the rings and make them all a size 6. It is easy to expand the size. I have expanded the 3" wrap ring up to a size 9.5.