Enable motherbord GPU in F15a BIOS with another GPU installed.

[Dan J]

So, all I'm wanting to do is to enable my motherboard GPU while there is a separate GPU installed. Most BIOS' that I have come across have a "Chipset" menu, with the option to force the GPU on, regardless as to whether there is another one installed, but for the life of me...I can't find the option anywhere in the F15A menu.
All I have are sub-menus labelled; Favourites(F11), Tweaker, Settings, System Info, Boot, and Save&Exit". I have looked through the sub-menus of each of these, but found nothing.
Any help would be appreciated. Thanks.