If you want to rotate an image around an arbitary point, you can make use of CGAffineTransform and it's MakeRotation method. This takes the angle in radians and then rotates the view to which it is applied.
For example to rotate an image approximately 30 degrees:
UIImageView imageView = new UIImageView (
new RectangleF(50,50, 250, 250)
);
imageView.Image = UIImage.FromFileUncached("/<path.to.image>/<image.name>");
imageView.Transform = CGAffineTransform.MakeRotation(0.5f);