To change the address format from the European default to i.e. the US format pick a locale in the media campaign:
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This address appears on the Cover Letter (on the Header, as well as in the table) as well as on the second page, under Contact Information. We support all locale which are also supported by Salesforce, for more information read: https://help.salesforce.com/articleView?id=admin_supported_locales.htm&language=en_US&type=0.