How do you repair rear hub assembly?

Not enough info here, but "hub" implies a hub, bearing, spindle with stud, they usually bolt on in one piece. Otherwise various models have different style hubs, some with replaceable bearings, flange, seals, etc and some come complete. A quick call to your local part store will provide the options you have, if it's a complete hub, it's usually remove drum/caliper, caliper bracket, rotor and hub may have a large hole in flange to allow socket to reach in and loosen bolts - again these are just guestimates based on average vehicles - your vehicle info is not included