Untitled

int selectedIndex = 0;

string[] menu = new string[]
{
    "Book",
    "Settings",
    "Exit"
};
Seat[,] aviaTickets = new Seat[6, 4]
{
            { new Seat("A1"), new Seat("A2"), new Seat("A3"), new Seat("A4") },
            { new Seat("B1"), new Seat("B2"), new Seat("B3"), new Seat("B4") },
            { new Seat("C1"), new Seat("C2"), new Seat("C3"), new Seat("C4") },
            { new Seat("D1"), new Seat("D2"), new Seat("D3"), new Seat("D4") },
            { new Seat("E1"), new Seat("E2"), new Seat("E3"), new Seat("E4") },
            { new Seat("F1"), new Seat("F2"), new Seat("F3"), new Seat("F4") }
};

while (true)
{
    Console.Clear();

    Console.WriteLine("Menu");

    for (int i = 0; i < menu.GetLength(0); i++)
    {
        if (selectedIndex == i)
        {
            Console.ForegroundColor = ConsoleColor.Blue;
            Console.WriteLine($"{i + 1}. {menu[i]} <<<");
        }
        else
        {
            Console.ResetColor();
            Console.WriteLine($"{i + 1}. {menu[i]}");
        }
    }

    ConsoleKeyInfo keyInfo = Console.ReadKey();

    switch (keyInfo.Key)
    {
        case ConsoleKey.UpArrow:
            if (selectedIndex > 0)
            {
                selectedIndex--;
            }
            break;

        case ConsoleKey.DownArrow:
            if (selectedIndex < menu.GetLength(0) - 1)
            {
                selectedIndex++;
            }
            break;

        case ConsoleKey.Enter:
            if (selectedIndex == 0)
            {
                Console.Clear();

                ShowSeats();

                Console.ReadKey();
            }
            else if (selectedIndex == 1)
            {
                Console.Clear();
                Console.WriteLine("Here are some settings");
                Console.ReadKey();
            }
            else if (selectedIndex == 2)
            {
                Console.Clear();
                Console.ResetColor();
                return;
            }
            break;
    }

    Console.ResetColor();

}

void ShowSeats()
{

    int selectedIndexY = 0;
    int selectedIndexX = 0;
    while (true)
    {
        Console.Clear();
        Console.WriteLine("Book");

        for (int i = 0; i < aviaTickets.GetLength(0); i++)
        {
            for (int j = 0; j < aviaTickets.GetLength(1); j++)
            {
                if (aviaTickets[i, j].IsBooked)
                {
                    Console.ForegroundColor = ConsoleColor.Red;
                }
                if (i == selectedIndexY && j == selectedIndexX)
                {
                    Console.ForegroundColor = ConsoleColor.Green;
                }
                else
                {
                    Console.ResetColor();
                }

                Console.Write($" [{aviaTickets[i, j].Name}] ");
            }
            Console.WriteLine();
        }

        ConsoleKeyInfo keyInfo = Console.ReadKey();
        switch (keyInfo.Key)
        {
            case ConsoleKey.UpArrow:
                {
                    if (selectedIndexY > 0)
                    {
                        selectedIndexY--;
                    }
                }
                break;
            case ConsoleKey.DownArrow:
                {
                    if (selectedIndexY < aviaTickets.GetLength(0) - 1)
                    {
                        selectedIndexY++;
                    }
                }
                break;

            case ConsoleKey.LeftArrow:
                {
                    if (selectedIndexX > 0)
                    {
                        selectedIndexX--;
                    }
                }
                break;
            case ConsoleKey.RightArrow:
                {
                    if (selectedIndexX < aviaTickets.GetLength(1) - 1)
                    {
                        selectedIndexX++;
                    }
                }
                break;
            case ConsoleKey.Enter:
                {
                    while (true)
                    {
                        Console.WriteLine("Для подтверждения нажмите любую клавишу ");
                        if (Console.ReadKey().Key == ConsoleKey.Enter)
                        {
                            aviaTickets[selectedIndexY, selectedIndexX].IsBooked = true;
                            break;
                        }
                    }
                }
                break;
        }
        Console.ResetColor();
    }
}

class Seat
{
    public string Name;
    public bool IsBooked;

    public Seat(string name)
    {
        Name = name;
    }
}