That is NOT easy. Soldering iron. Heat the pin and pull the wheel and hub off. Repeat with Junkheap. Usually the pin stays. Heat it up for like 15 secs and quickly get pliers to pull it out. Let the pin cool down. Push it into the wheel hub. Put the hub into the wheel and carefully place the whole thing over the rear axle hole. Use the soldering iron and heat up the pin as you push it back in.