I can't change the mouse for left-handed people using the computer.

You need to install the xorg-xmodmap package to configure the mouse buttons.

Install the xorg-xmodmap package. In a terminal, type:

# tazpkg -gi xorg-xmodmap

To configure the mouse for left-handed:

# xmodmap -e "pointer = 3 2 1"

To configure the mouse for right-handed:

# xmodmap -e "pointer = 1 2 3"

To check the configuration of your mouse:

# xmodmap -pp

To make the changes permanent for your user, create a new file called xmodmap.desktop in the ~/.config/autostart directory with the following content:

[Desktop Entry]
Type=Application
Name=Left hand mouse
Exec=xmodmap -e "pointer = 3 2 1"
NotShowIn=XFCE;Razor;LXDE;

Logout and Login to X session and the mouse buttons are configured for left-handed people.

To make the changes permanent for all users at the same time, repeat the procedure above as root, creating a new xmodmap.desktop file in the /etc/xdg/autostart directory.

References:
Mouse left-handed
Configure left-handed mouse