The sample code for generating random letters in C# is given below...

namespace ConsoleApplicationTest
{
    class Program {

        static void Main(string[] args) {

            Random random = new Random();
            
            int letNum = random.Next(0, 26);
            char chr = (char)('a' + letNum);

            Console.WriteLine(chr);

            Console.ReadLine();

        }
    }
}