encrypt the app.config connectionstring

I am trying to encrypt the connection string in a win form and I found this code on Expert Exchange. I encrypted the connection string but how do I put the encrypted string in the config file?
code to get encrypted string

 private void Form1_Load(object sender, EventArgs e)
        {
            string conString = ConfigurationManager.ConnectionStrings["MyConString"].ToString();
            textBox1.Text = vault.Encrypt(conString);
            
        }

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Encrypted string

7sIgbZ0r6wGpIahLvIZrJmCjYAJNJGMno464rU6TMaimMYfOKAxZD2NyPYgT76/J09BUqjeT9/1X9ZfvbaY7rKYCBz2H+xqE2PWStpQJ3Da9nENakNNqx683yj5EEp514CKaVG7EUw4MiUG9ASNKLjUcnVyw340Vpu0PSNjMMs/WoZS/zQvy8CFXZtpvOS+C

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Encryption/decryption code

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;


namespace EncryptTest
{
    class vault
    {
        /************************************************************************************************************************************/
        #region Public Methods

        public static string Encrypt(string plainText)
        {
            RijndaelManaged key = GetKey();
            byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);
            using (ICryptoTransform encryptor = key.CreateEncryptor())
            {
                using (MemoryStream memoryStream = new MemoryStream())
                {
                    using (CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
                    {
                        cryptoStream.Write(plainTextBytes, 0, plainText.Length);
                        cryptoStream.FlushFinalBlock();
                        
                        return Convert.ToBase64String(memoryStream.ToArray());
                    }
                }
            }
        }

        public static string Decrypt(string encryptedString)
        {
            RijndaelManaged key = GetKey();
            byte[] encryptedData = Convert.FromBase64String(encryptedString);
            using (ICryptoTransform decryptor = key.CreateDecryptor(key.Key, key.IV))
            {
                using (MemoryStream memoryStream = new MemoryStream(encryptedData))
                {
                    using (CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))
                    {
                        byte[] plainText = new byte[encryptedData.Length];
                        int decryptedCount = cryptoStream.Read(plainText, 0, plainText.Length);
                        return Encoding.UTF8.GetString(plainText, 0, decryptedCount);
                    }
                }
            }
        }

        #endregion
        /************************************************************************************************************************************/
        #region Private Methods

        //Create encryption key
        private static RijndaelManaged GetKey()
        {
            RijndaelManaged key = new RijndaelManaged();
            byte[] passwordBytes = Encoding.UTF8.GetBytes(Properties.Resources.Password);
            byte[] saltBytes = Encoding.UTF8.GetBytes(Properties.Resources.Salt);
            PasswordDeriveBytes p = new PasswordDeriveBytes(passwordBytes, saltBytes);
            key.IV = p.GetBytes(key.BlockSize / 8);
            key.Key = p.GetBytes(key.KeySize / 8);
            return key;
        }

        #endregion
        /************************************************************************************************************************************/
    }
}

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