Sheet metals, especially those of the softer metals like copper are notorious for breaking when straightening a piece that is creased, (such as the disc fitted behind the guard.) If you do attempt this, my advice would be slowly and gently, perhaps using pliers to grip and lever the piece, this will give you more control. Ensure that the jaws of the pliers are protected by thickish cardboard (not corrugated), this will help prevent marking the softer metal of the 'disc.' It won't be a perfect repair, but will give a more acceptable appearance..... Hope this helps
