Minecraft secondary GPU Ofload

Using 2 GPUs is called SLI. Minecraft doesn't need or even support the feature. If you're having FPS issues in Minecraft, this is likely to be because of your CPU, which Minecraft (especially when modded) uses a lot more than the GPU.

Check first through task manager whether it's really your GPU that's holding you back. This can be checked by finding the Java process that's running Minecraft and seeing whether CPU or GPU is under a higher load from the process. If the GPU has the higher load, and you're using a texture pack, see if there's a less resource intensive version of your texture pack (example: if your texture pack currently is 128x128, see if 64x64 improves performance). If it's the CPU, and youre playing modded, you'll probably have to uninstall some of them or scale down your special block usage near your location.