Should be able to right click on desktop and choose graphics properties or something like that. Go into AMD's switchable graphics section and select the exe files for the game and set it to high performance. (you will have to go to c drive, x86 program files, game folder, game executable (application file)). Sorry as I can't give precise instructions as I've only seen this done once on an AMD gpu computer.
Also make sure you computer is in balanced or high performance mode (power/battery icon).