pnp/pci slots

I would like to know how to reset the configuration of the pnp/pci slots on the mother board. I have tried to reset it through the bios setup in “pnp/pci configuration ” menu. did not work. want to reinstall a card and cannot due to previous installation. I would like windows to detect new harware automatically as it does when the slot is first used.what do I do to get the slot in the unused state?