how to change wording of "new address button"

Hi,

Like any text in HikaShop, you can edit your translation file via the interface in the languages tab of the config and override the translation.
However, the "New" text is a generic text which is used in a lot of places. If you change it to "Add a new address", that will change it everywhere which is not what you want.
So you need to edit the file address_view of the view checkout via the menu Display->Views and change directly the code JText::_('HIKA_NEW') by your text "Add a new address" so that it is replaced only there.