Your default return address, which is also the business address associated with your selling account, will be used on all returns, unless you select an alternative return address when you authorize a return.
If your seller account is set up as an Amazon European Marketplaces account, your default return address will be shared across Amazon.co.uk, Amazon.fr, Amazon.de, Amazon.it and Amazon.es. However, you can add a specific return address for any of the marketplaces you sell in. To do so, at the very end of the page, click on "Add a new exception for another marketplace". The address you enter in the Exception Marketplace section will be printed on the return label for return requests in that selected marketplace.