In order to receive the replacement disc, a Let's Go to the City owner must contact Nintendo Australia Customer Support and give them the serial numbers of their game and their Wii console. Once Nintendo has this information, they will send out an express post bag for players to ship off their defective discs, after which Nintendo will send a brand new disc.
Sadly, players who have already started up a game in Animal Crossing: Let's Go to the City will need to begin again if they wish to use their Wild World data.