You do nothing. That card can accellerate NOTHING in AE.
As Dave says, GPU does very little in AE, see this: GPU (CUDA, OpenGL) features in After Effects
Now, some third-party plugins (such as Red Giant Universe and Video Copilot's Element 3d) do make use of the GPU in AE, but their requirements have nothing to do with AE or its settings.
Premiere, on the other hand, does make use of a GPU, you should ask in that forum what they suggest.
Also, in the future, I would suggest checking on system requirements and benefits BEFORE making a purchase...
PP CS6 requires editing the CUDA.txt file with the 980GTX card listing. There are many walkthroughs online for that.