How to create a class of method for oracleconnection in a C# so that it can be reused for next database to be fetched

using System;
using System.Collections.Generic;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using Oracle.DataAccess;
using Oracle.DataAccess.Client; //ODP.NET ORacle managed provider

namespace WindowsFormsApp7
{
    public partial class MyApp : Form
    {

        public MyApp()
        {
            InitializeComponent();
        }

        private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
        {

        }

        private void Form1_Load(object sender, EventArgs e)
        {
            string OracleServer = "Data Source=mydb;"
            + "User Id=Config;Password=config123;"; //  your username and password database server

            OracleConnection conn = new OracleConnection(OracleServer);
            conn.Open();
            string orcl = @"Select * FROM mydatabase";
            OracleCommand cmd = new OracleCommand(orcl);

            cmd.Connection = conn;
            OracleDataAdapter da = new OracleDataAdapter();
            DataTable dt = new DataTable();
            da.SelectCommand = cmd;
            da.Fill(dt);

            listBoxdB.DataSource = dt;
            listBoxdB.ValueMember = "Database_id";
            listBoxdB.DisplayMember = "Location";

            this.dataGridView1.DataSource = dt;
            this.dataGridView1.Refresh();


            conn.Close();
            conn.Dispose();
        }

        private void listBoxdB_SelectedIndexChanged(object sender, EventArgs e)
        {
            string strDbID = Convert.ToString(listBoxdB.SelectedValue);
            string strDbLocation = Convert.ToString(listBoxdB.GetItemText(listBoxdB.SelectedItem));

            string strSql = @"select Name, id from my_source
                            where id not in (select id
                            from new_database
                            where database_id = " + strDbID + ")";

            string OracleServer = "Data Source=mydb;"
                                   + "User Id=config;Password=config123;"; 

            OracleConnection conn = new OracleConnection(OracleServer);
            conn.Open();
            OracleCommand cmd = new OracleCommand(strSql);
            cmd.Connection = conn;
            OracleDataAdapter da = new OracleDataAdapter();
            DataTable dt = new DataTable();
            da.SelectCommand = cmd;


            try
            {
                da.Fill(dt);

                this.listBoxApp.DataSource = dt;
                this.listBoxApp.ValueMember = "Application_id";
                this.listBoxApp.DisplayMember = "Application_Name";

            }
            catch { }

        }


        private void listBoxApp_SelectedIndexChanged(object sender, EventArgs e)
        {

        }
    }
}