You can either install a newer driver version for your card, or install the previous driver 16.11.5 if you want to have the "additional settings" feature. Or, you could try this > Can't open Radeon Additional Settings...Part 3 A FIX !!
New Features and Improvements
- Radeon Additional Settings has been retired and its previously supported controls for Switchable Graphics, Color Depth and Pixel Format have all been moved into Radeon Settings.