Hello,
You mean XP-Pen … and you downloaded a *.tar.gz file from their site, right? Might depend on the tablet model tho. Extract the content of that archive, enter in that folder and open Terminal in that folder. Then you run:
sudo ./install.sh
I think you might have to then run:
sudo chown $(whoami) /usr/lib/pentablet
and ten
sudo chmod +x /usr/lib/pentablet/pentablet
Reconnect your tablet, or reboot the system and you will have the app working and the UI to configure the express keys and map/callibrate it.
Edit: There is an AUR package for it AUR (en) - xp-pen-tablet
You run from terminal:
pamac build xp-pen-tablet
type y for yes and press Enter to continue, and you should be good to go after that.