Dual Monitor Problem. I need help. I was trying to set up dual monitor on our church computer and

Question

I need help. I was trying to set up dual monitor on our church computer and messed it up. The computer monitor is now identified as monitor 2 and the video screen is identified as Monitor 1. The desktop of the pc now shows on the video screen. I know there is a keyboard shortcut, at least there was on a laptop I used several years ago. This is a desktop computer by emachines that I use at church.