Change a default

Casey,

If this is a field that is being updated by a smart campaign, you can navigate to the "Campaign Inspector" and search for the field. The resulting list will show all smart campaigns referencing that field and you can find the one updating that value.

Campaign Inspector will first need to be enabled in Admin > Treasure Chest. Then in Marketing Activities, click the topmost "Marketing Activities" icon in the navigation tree. Campaign Inspector will be the second tab.

While not an answer to your question, if you're using the same value across multiple smart campaigns, you should consider using a token to easily manage updating it centrally

You can identify the leads which have the incorrect default address, and look at the activity log of these leads. It will tell you which campaign changed the default address incorrectly. So you can go and fix that particular campaign.