Back Office
Navigation: Log into the Back Office for your Store, then select Settings > Application > General Settings
The Disable Customer Nationality toggle will be enabled (set to YES) by default.
If set to YES, the Nationality field will not appear on the Customer Profile screen in the POS.
If set to NO, it won't appear.
POS
New Customer
Click Add New.
If the Disable Customer Nationality toggle was set as NO: the Nationality field appears, where you can select the nationality from the dropdown list.

Click Save, and the nationality will be added to the customer's profile.
Existing Customer
If the Disable Customer Nationality toggle is Yes, the Nationality field does not appear on the customer's profile.
If the Customer was created without a Nationality: you cannot add a Nationality for that existing customer - even if the Disable Customer Nationality toggle is set as NO in BO.
For an existing Customer: when the toggle is No in BO you can change the nationality by clicking the Nationality field.