You can install touchpad-indicator by downloading the .deb file. Once downloaded, just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, navigate to the folder where the file was downloaded, and run the command below:
sudo dpkg -i <package_name>
Now keep in mind if you get the error below:
touchpad-indicator depends on gir1.2-gconf-2.0; however:
Package gir1.2-gconf-2.0 is not installed.
touchpad-indicator depends on python-pyudev; however:
Package python-pyudev is not installed.
You can download Package gir1.2-gconf-2.0 here, and Package python-pyudev here