How do I use update code in C# while using GUI

private void button2_Click(object sender, EventArgs e)
 {
     try
     {
         if (textBox1.Text == "" || textBox2.Text == "" || comboBox1.Text== ""|| textBox3.Text == "")
         {
             MessageBox.Show("Missing information");
         }
         else
         {

             Con.Open();
             if (int.TryParse(textBoxCId.Text, out int CId))
             { 
             SqlCommand cmd = new SqlCommand("UPDATE EventTbl SET CName=@CN,CPhone=@CP,Events=@E,Date=@D WHERE CId=@key", Con);
             cmd.Parameters.AddWithValue("@CN", textBox1.Text);
             cmd.Parameters.AddWithValue("@CP", textBox2.Text);
             cmd.Parameters.AddWithValue("@E", comboBox1.Text);
             cmd.Parameters.AddWithValue("@D", textBox3.Text);
             cmd.Parameters.AddWithValue("@key", CId);
             cmd.ExecuteNonQuery();
             Con.Close();
             MessageBox.Show("Record Update Sucessfully");
             DisplayEvent();
             }
             else
             {
                 MessageBox.Show("Invalid CId. Please enter a valid integer value.");
             }

         }
     }
     catch (Exception ex)
     {
         MessageBox.Show(ex.Message);
     }
     finally { Con.Close(); }
 }