How do I put my public void code into a main code?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace BankAccount2
{

    class Program
    {
        static void Main(string[] args)
        {

            int bankMenu; // Making a variable that I will later use for a swtich statement

            Console.WriteLine("Welcome to Ernie's Bank");
            Console.WriteLine("Let's start of with your registery.\n");
            Console.Write("Your first name :");
            string firstName = Console.ReadLine(); // Letting the user assign his name to the variable firstName
            Console.Write("Your last name :");
            string lastName = Console.ReadLine(); // Repeating the process

            BankAcc user = new BankAcc(firstName, lastName); // I am using the class to 
            

            Console.Clear();

            Console.WriteLine("So your name is : " + firstName + "\nAnd your last name is : " + lastName); // Printing out the users name

            Console.Write("Press any key to continue");
            Console.ReadLine();
            Console.Clear();



            do 
            {
                Console.Clear();

                Console.WriteLine("This is Ernie's Bank Menu!");
                Console.WriteLine("1. Deposit\t2. Withdrawal\t3. Current Balance\n4. Exit"); // Printing out the options
                Console.Write("\n\nChoose an option from the menu : ");

                while(!Int32.TryParse(Console.ReadLine(), out bankMenu)) //Bullet proofing the code
                {
                    Console.Clear();

                    Console.WriteLine("So this is Ernie's Bank Menu!");
                    Console.WriteLine("1. Deposit\t2. Withdrawal\t3. Current Balance\n4. Exit\n\n");
                    Console.WriteLine("Valid option's only!");
                    Console.Write("Choose an option from the menu : ");
                }

                switch (bankMenu) // Making a switch statement since I am letting the user choose what he wants to do 
                {
                    case 1:
                        
                        break;
                    case 2:
                        Console.WriteLine("You chose Withdrawal!");
                        
                        break;
                    case 3: // This case is to display the user's balance
                        user.DisplayBalance();
                        Console.Write("Press any key to continue...");
                        Console.ReadLine();
                        break;
                    case 4: // This statement is the exit
                        Console.Clear();
                        Console.WriteLine("You chose Exit");
                        Console.WriteLine("\nHave a nice day " + firstName + "!");
                        Console.Write("Press any key to continue...");
                        Console.ReadKey();
                        break;
                    default:
                        Console.WriteLine("Hey! That ain't a option my man");
                        Console.WriteLine("\nPress any key to continue...");
                        Console.ReadKey();
                        break;
                }
            } while (bankMenu !=4);

And I made a class that looks like this : 

namespace BankAccount2
{
    class BankAcc
    {
        private string firstName = "";
        private string lastName = ""; //Making the variables
        private float balance;

        public BankAcc(string firstName, string lastName)
        {
            this.firstName = firstName;
            this.lastName = lastName;
            balance = 50000; // Giving the user a start balance of 50000

        }

        public BankAcc(string firstName, string lastName, float balance)
        {
            this.firstName = firstName;
            this.lastName = lastName;
            this.balance = balance;

            
        }

        public string FirstName
        {
            get // Getting his first name and then returning
            {
                return firstName;
            }
             // Setting his first name as a value
            set
            {
                firstName = value;
            }
        }

        public string LastName
        {
            get // Repeating the process from the FirstName
            {
                return lastName;
            }

            set
            {
                lastName = value;
            }
        }

        public float Balance
        {
            get // Getting the balance and then returning it. Later on I give a balance a initial value
            {
                return balance; 
            }

            set
            {
                balance = value;
            }
        }

        public void Deposit(float amount)
        {
            Console.Write("Choose an amount to deposit :");

            balance += amount;
        }

        public void Withdraw(float amount)
        {
            Console.Write("Choose an amount to withdraw");

            if (amount > balance) // If the user tries to withdraw more than his funds it will tell him insufficient funds
            {
                Console.WriteLine("Insufficient funds...");
            }
            else
            {
                balance -= amount;
            }
        }   

        public void DisplayBalance()
        {
            Console.WriteLine($"Your current balance is {balance}ISK."); // Displaying his balance
        }

    }
}