I imagine that this will be different for everyone depending on your hardware configuration...
For me, a link to the Nvidia driver is in the 'quick-link' box (that's not the official Microsoft name for it), appearing when you mouse over the arrow on the left-hand side of the taskbar. By clicking on that icon, I get the option to 'customize which programs use the GPU'. Selecting that option opens a control panel, which gives me the option of 'adding' a program. When I select add, a new window opens with a list of my programs. Then I selected 'dogfight' et voila, it runs successfully on the GPU.