Enable Pre-Order by Countries for Whole Store
IMPORTANT NOTE: If this setting is made, all enabled Pre-Orders will only be available to the specified countries.
Go to Settings. Under App Settings, look for Pre-Order Locations:
Select the dropdown and untick on "All countries".
Search the countries by typing on the search column and select the countries you want to apply the pre-order to:
Customers coming from outside the selected countries will see a Sold Out instead of Pre-Order instead.
Enable Pre-Order by Countries for Individual Products
At the Products page, select the Default Settings (or Custom Settings) button of the product you wish to configure:
At the Pre-Order tab, turn on Pre-Order Locations and select the country you want to apply pre-order to and select Save:
IMPORTANT NOTE: This setting will apply for individual products only.