Well, (assuming you are using X11) i don’t know what you have tried, however there is the usually good Arch Wiki:
https://wiki.archlinux.org/title/Setxkbmap
The manual pages:
man setxkbmap
man xkbcomp
you could also try editing the keyboard file in /etc/default :
sudo nano /etc/default/keyboard
CTRL + o (enter) to save
CTRL + X (enter) to quit
edit: added the ‘assuming you are using X11’ part)