When on ArchMerge you can set your touchpad with the gui of XFCE settings or keyboard shortcut
CTRL + ALT + M.
This will work on Xfce and Openbox. If you want to have this solution on i3 you will need to delete a hashtag in the config file.
#exec --no-startup-id xfsettingsd &
When you are on ArchMergeD with any of the possible desktops you need to check this page. https://wiki.archlinux.org/index.php/Libinput.
Some of the desktop environments provide you some kind of settings manager for your touchpad and in others you will have to make a configuration file for your touchpad in
The content is up to you but could be something like this.
Option "Tapping" "on"
If libinput fails to work on your hardware, you can also have a look at this wiki page but it is NOT encouraged.