How to do it...

1. Open your AL project folder in Visual Studio Code.
2. In Visual Studio Code's Explorer pane, right-click and create a new file named Customer Extension.al. In the Editor tab, add the code as follows:

tableextension 50100 CustomerExtension extends Customer
{
    fields
    {
        field(50100; "Television Viewing Country"; Option)
        {
            DataClassification = CustomerContent;
            OptionMembers = Canada,"United States","United 
            Kingdom";
        }
    }
}

1. Close and save the Customer Extension.al file.