How change monitors from terminal ? "xrandr: Cant open display"

I'm booting Sparkylinux from a live-usb in a notebook with broken screen. There is a external monitor connected by VGA. The external monitor is booted dual with the notebook monitor And the external monitor resolution is booted with some issues. To fix it i need to put the external monitor as the primary monitor, or even better, shutdown the notebook monitor. In Ubuntu i can use Fn key to change monitors. In Lubuntu, even i cant see much, i can open the start menu, type monitor and change it manually. In Sparkylinux the special key dosen't work and start menu is tricky, so i cant access the monitor menu whithout seeing. So I'm trying xrandr to change it , but apearently i cant open the terminal ( ctrl+alt+t), the bad resolution sends it to another realm. So i used ctrl+alt+F1 to try xrandr, but for most but not all xrandr commands i get "xrandr: Cant open display". Like xrandr --listmonitors