As far as I know, UE4 has only one official implementation for Dynamic GI, and it is called LPV (Light propagation volumen):
You could alternatively use Nvidia’s VXGI, but you will have to download that branch from GitHub, compile and build the engine.
https://forums.unrealengine.com/community/general-discussion/90111-nvidia-vxgi-integration
To me the second one gives better results, but its way more buggy.
By default you don’t have dynamic GI, what you have is screen space effects like reflections and AO, which gives a hint of dynamic GI but it is not.