I was wondering how to redirect back to the settings.aspx page.

Here is what worked like a charm for me.

/// <summary>
/// Event that is raised when the user clicks on OK Button
/// </summary>
/// <param name="sender" />Sender of the event</param>
/// <param name="e">Arguments of the event</param>
private void BtnOk_Click(object sender, EventArgs e)
{
  // Do nasty stuff here
  // ...
 
  // Redirect to settings page if data is valid
  if (IsValid)
  {
    SPUtility.Redirect("settings.aspx", SPRedirectFlags.Static | SPRedirectFlags.RelativeToLayoutsPage, HttpContext.Current);
  }
}