As I said in the comments, you could embed it in a while loop
bool continue = true;
while (continue)
{
    Console.WriteLine("Enter Customer Details (s)"); 
    Console.WriteLine("Enter usage data (u)"); 
    Console.WriteLine("Display usage data (d)");
    Console.WriteLine("Exit (e)");
    string menu = Console.ReadLine();
    switch (menu)
    {
        case "s":
            //statement 
            break;
        case "u":
            //statement 
            break; 
        case "d":
            //statement 
            break; 
        case "e":
        default: 
            continue = false;
            break;
    }
}
solved Switch statements for a Menu (c#)