Easy Country Blocker App allow users to select which countries to block or to create rules based on specific criteria, while others may have a fixed set of countries that are blocked.
You can customize the Blocked countries list. You can remove that country from where country is blocked.
Overall, by using this app you can customize the list and you can block and unblock the countries at the same time.
Install the app from here.
Shopify : https://apps.shopify.com/country-blocker-1
Bigcommerce : https://www.bigcommerce.com/apps/easy-country-blocker/