You can change the default auctioneer address by going into the Auctioneer settings. Click here to find out how to access your Auctioneer settings.
Once you are editing your Auctioneer, go to the Contact Address tab. Here you will find address fields that can be filled in to represent your address within the auction:
When you have made any changes as required, click the green Save Auctioneer button at the top of the screen.