Using this amazing project tmate.io you can SSH tunnel to your colab notebook machine. You can with few lines of code download the binary, run an instance in the background and output the generated SSH address.
!wget -nc https://github.com/tmate-io/tmate/releases/download/2.4.0/tmate-2.4.0-static-linux-i386.tar.xz &> /dev/null
!tar --skip-old-files -xvf tmate-2.4.0-static-linux-i386.tar.xz &> /dev/null
!rm -f nohup.out; bash -ic 'nohup ./tmate-2.4.0-static-linux-i386/tmate -S /tmp/tmate.sock new-session -d & disown -a' >/dev/null 2>&1
!./tmate-2.4.0-static-linux-i386/tmate -S /tmp/tmate.sock wait tmate-ready