How do I extend a WinForm’s Dispose method?

You need to override the Dispose method from Form

Typically this is automatically overridden in the RestartForm.Designer.cs file, so you will need to move the dispose into your code file so that you can add whatever code you need to add without it being rewritten by the designer.

In the RestartForm.cs

protected override void Dispose(bool disposing)
{
  if (disposing)
  {
    if (components != null)
    {
      components.Dispose();
    }

    // Dispose stuff here
  }

  base.Dispose(disposing);
}