CMOS question

Hi everybody. I just fired up my new Microtel gamer and as usual I couldn't resist going into CMOS to try to see why it wasn't seeing my Radeon HD 7870 GPU. I found a setting with 2 choices. Both with 3 letter designations. Wish I could remember what they were to help with a workaround. I switched to the other setting and now I have no video at all. The MB is a MSI z77a-g41. How the hell do I get into CMOS to change it back when I have no video?

Thanks: Mark