// Method to modify a specific customer which exists in the crm file
        public void ModifyCustomerSubmenu(bool clear = true)
        {
            if (clear)
            {
                Console.Clear();
            }

            Console.WriteLine("### Modify Customer Submenu ###\n");
            ModifyCRMValidationInput();
            // Return the customer which matches the provided ID to modify and assign to modifiedcustomer object
            Customer customer = Crm.GetCustomer(IDtoMofify);

            // if the returned customer in the modified customer object is not null, proceed to modify
            if (customer != null)
            {
                // Store old customers ID, title, first and last names into variables
                int    OldID = customer.ID;
                string OldTitle = customer.title, OldFirstName = customer.firstName, OldLastName = customer.lastName;
                // Set the customer ID to the highest id value + 1, in case the customer wants to retain his/her ID and only wants
                // to modify the fields. We set the ID to this so that the validation doesnt prompt an error that the ID wanting
                // to be retained already exists. If the ID is retained, there is still unique ID's in the list
                int HighestID = Crm.CustomerList.Max(Customer => Customer.ID) + 1;
                customer.ID = HighestID;
                // Save the changed ID value in case customer decideds to retain the same ID in the modification menu.
                Crm.SaveToFile();
                ModifyIDValidationInput();
                customer.ID = IDtoMofify;
                Console.Write("Title*: ");
                title          = StringToTitleCase(Console.ReadLine());
                customer.title = title;
                Console.Write("FirstName*: ");
                firstName          = StringToTitleCase(Console.ReadLine());
                customer.firstName = firstName;
                Console.Write("LastName*: ");
                lastName          = StringToTitleCase(Console.ReadLine());
                customer.lastName = lastName;
                GenderValidationInput();
                customer.gender = Gender;
                DOBValidationInput();
                customer.DOB = DOB;
                Console.Write("\nSuccessfully modified customer '{0} - {1} {2} {3}' to '{4} {5} {6} {7}' within the customers list",
                              OldID, OldTitle, OldFirstName, OldLastName, IDtoMofify, title, firstName, lastName);
                Crm.SaveToFile();
                LastMRRCscreen(() => SubMenu("Customer"), () => ModifyCustomerSubmenu());
            }
            // If the returned customer in the object is null, then the customer does not exist
            else
            {
                Console.Clear();
                Console.WriteLine("Customer with an ID of '{0}' does not exist in the Customers List\n", IDtoMofify);
                ModifyCustomerSubmenu(false);
                LastMRRCscreen(() => SubMenu("Customer"), () => ModifyCustomerSubmenu());
            }
        }