How to allow only a country to access my site?

You can do that by following these steps:

Step 1: Go to the "Blocker & Redirector" tab, select "Block" and click "Block country". In the pop-up, select "Add all countries" to block access from every country and click "Add".

Step 2: Select "Whitelist" and click "Whitelist country". In the pop-up, select a country or every country that you want to allow access from and click "Add".