You just need to buy a properly sized bolt and nut to replace the stud.
Use the double nut jam trick to turn out the broken stud if there's threads left attached to it, or drill it out if it snapped off flush. While you're at it, I'd replace both studs with the nut and bolt so they match.
Use the double nut jam trick to turn out the broken stud if there's threads left attached to it, or drill it out if it snapped off flush. While you're at it, I'd replace both studs with the nut and bolt so they match.