Read the warranty information if you still have it. The manufacturer's warranty often covers ring repairs and replacements. Services normally covered include repairs to defects in workmanship or materials and resizing, among other things.
Contact the ring's manufacturer. The company can advise you about what steps you need to take to repair the ring.
Mail the ring to the designated place of repair as suggested by the manufacturer or retailer. Make sure you insure the ring. Obtain a tracking number at the post office before shipping it.
Take the ring to a jeweler for a repair estimate. If the ring had a stone and you still have it, make sure you have everything with you. Before considering this option, make sure the original warranty is no longer applicable. As with most other merchandise, an unauthorized repair on a ring will nullify the original manufacturer's warranty.