Connection string and Openfiledialog

I want change the connection string automatically when user select file with Openfiledialog. How do I that?

// Form1. The connection string is set same as selected with Openfieldialog
SqlConnection sqlConn = new SqlConnection("Data Source=(LocalDB)\\MSSQLLocalDB;AttachDbFilename=C:\\xxx.mdf;Integrated Security=True;Connect Timeout=30");

//Form2
private void button2_Click(object sender, EventArgs e)
        {
            Stream myStream = null;
            OpenFileDialog openFileDialog1 = new OpenFileDialog();

            openFileDialog1.InitialDirectory = "c:\\";
            openFileDialog1.Filter = "mdf files (*.mdf)|*.mdf";
            openFileDialog1.FilterIndex = 2;
            openFileDialog1.RestoreDirectory = true;

            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                try
                {
                    if ((myStream = openFileDialog1.OpenFile()) != null)
                    {
                        using (myStream)
                        {
                            // Insert code to read the stream here.
                        }
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show("Error: Could not read file from disk. Original error: " + ex.Message);
                }
            }
        }