The transaction DBAPTA is allowed to create a associated address to the main party.

Launch the transaction DBAPTA from menu Static Data -> Parties -> Main -> Party Address.

(Users can also directly start this transaction by clicking the  (Launch transaction ) available in the Panel headline without having to select the relevant menu) 

To create a new party click the + icon.

When you have made your changes, click on the ( )  Save function to save all the the data entered in the transaction to the database.