The return address on your Royal Mail 2D Barcoded labels is set by NetDespatch and can't be edited in Zenstores I'm afraid.

Luckily its really easy to get it updated and changed, simply pop an email over

In the email provide them with your NetDespatch user ID (this should have been emailed to you by us when your integration went live in your Zenstores account) and then the new or updated address that you want as your return address.

And thats all you have to, NetDespatch should let you know via email once they have updated your return address and then your good to go.