Default invoice addresses are entered in the Account on the Added Fields tab. Whenever an event is created, this invoice address will be suggested for the event.
Open the organiser's Account.
Go to the Added fields tab in the side navigation.
Go to the Invoice to field and enter the name of the invoice address, select the right account from the list of results and Confirm. Alternatively, enter a new account.
Save your input by clicking on the icon in the top left-hand corner of the input window.