You may have to manually add your GPU to the "FAHControl" application, but it's quite simple. Just open "FAHControl", select the "Configure" button in the top left corner, navigate to the "Slots" tab and check the GPU box (picture below).
You can leave the other options aside, the software will take care of it for you.
If you don't have a dedicated graphics card, the Folding@Home team is working on adding COVID-19 simulations to CPU workloads as well, but no timeline has been given for that.
Need some technical help? Jean-Daniel can help: firstname.lastname@example.org