✅ How to Update the original instance of my Main Form from another form

public void showMacro() //Funktion die alle Dateien im macro Pfad in einer ListBox auflistet
{
    MessageBox.Show("test");
    if (Directory.Exists(macroPath))
    {
        string[] files = Directory.GetFiles(macroPath);
        ltxMacroShowCase.Items.Clear();

        foreach (string macro in files)
        {
            ltxMacroShowCase.Items.Add(Path.GetFileName(macro));
        }
    }
}

private void btnOkay_Click(object sender, EventArgs e)
{
    try
    {
        Form1 f1 = new Form1();

        File.WriteAllText(Path.Combine(Form1.macroPath, txbNameInput.Text), "");
        f1.showMacro();
        this.Close();   //erfolgreiches erstellen der macro Datei

    }
    catch (Exception ex)
    {
        MessageBox.Show("this is not a valid Name! " + ex.Message);
        return;
    }
}