The simplest way, which found on the google, is to create a script:
Save it and run it every time start up desktop.synclient TapButton2=2 synclient TapButton3=3
Or you can modify/usr/share/X11/xorg.conf.d/50-synaptics.conf:
Section "InputClass"
Identifier "touchpad catchall"
MatchIsTouchpad "on"
MatchDevicePath "/dev/input/event*"
Driver "synaptics"
Option "VertTwoFingerScroll" "on"
Option "HorizTwoFingerScroll" "on"
Option "CircularScrolling" "off"
Option "CricularTrigger" "0"
Option "TapButton1" "1"
Option "TapButton2" "2"
Option "TapButton3" "3"
EndSection
I'm lazy to do that.
