First you need to reinstall your gnome-shell

sudo apt-get install --reinstall ubuntu-gnome-desktop

Then install gnome extension manager

sudo apt install gnome-shell-extension-manager

Now open the extension manager

Now search for X11 Gestures exntension and install it

lastly run these to enable it

sudo add-apt-repository ppa:touchegg/stable
sudo apt update
sudo apt install touchegg