To change the country availability, sign in to your Developer Portal and go to the Apps & Services menu. Once there, select the app you wish to edit for country availability, and click on the "Availability and Pricing" tab. On this tab, uncheck the box next to the country in which you do not want your app to be sold. The default will be to make your app available in all countries in which Amazon offers apps.
Finally, click the "Save" button to save your changes and the "Submit App" button to submit your app for review.