HDMI output for Recalbox on USB key

[OliLef]

Hi,
HDMI output is not correct from Recalbox on USB key.
I'd like to follow instructions from https://github.com/recalbox/recalbox-os/wiki/Change-display-resolution-on-x86---x86_64 but xrandr command returns "Can't open display" message, even when I try to export display variable with export DISPLAY=:0 command.
What could I try please ?

[OyyoDams]

please don't double post

https://forum.recalbox.com/topic/16582/sortie-hdmi-pour-recalbox-sur-clé-usb/13