How do i add Options to the xorg conf?

Where is, and how do I change the xorg conf file? I want to change the default scrolling speed of my touchpad. I can use xinput --set-prop "YOUR TOUCHPAD" "libinput Scrolling Pixel Distance" YOUR_SPEED to change it for this session, but I would like to make it permanent. I've read here https://man.archlinux.org/man/libinput.4#Option~24 , that I can change the Option "ScrollPixelDistance" "int" but I don't know how to do this or where to find the xorg config file.