The quickest way to improve your gaming performance is to sell your Mac and buy a gaming PC.
Joking aside, if you look at the performance benchmarks of the GPU it's not really for gaming. It's for content creation. If you are however doing more gaming than anything else, I'd say a Mac isn't the right platform for that and there's not much you can do to improve the performance of your laptop. Getting an external TB3 enclosure with a GPU in theory works, but it's not exactly portable.