I search a bit and according to this you need to allow the root user access to X server and point to the right display.

use this commands


And then this


If not, try to repeat the installation try to follow the guide from their Github here https://github.com/goatpig/BitcoinArmory/blob/master/linuxbuild/Linux_build_notes.md
Just take note of the version on the commands so replace it with the latest firmware version.