I keep forgetting where to find this whenever I install a new Linux distro with KDE as the desktop environment.
Some distrobutions — like Linux Mint — come prepackaged with a nice touchpad management section under their settings panel (input devices). But, others — like Manjaro — don’t.
The package you’re looking for is called
On an Arch-based distro, it’s in the repo’s here:
sudo pacman -S kcm-touchpad
I’m sure it’s also hanging around in whatever package repository your distro comes with. It’s a few years old now.