how to rollback in ubantu code example

Example: rollback ubuntu system

##FOR DEBIAN:
$ sudo add-apt-repository "deb http://ppa.launchpad.net/nemh/systemback/ubuntu xenial main"

# OR For Whatever flavor of Ubuntu you currently use:
$ sudo add-apt-repository "deb http://ppa.launchpad.net/nemh/systemback/ubuntu focal fossa main"

## Simply replace the flavor name with the flavor you are using. i.e.
## groovy; focal fossa, etc.

## Just a quick note of interest:
# You can login as a sudoer or as root from the start of opening the
# terminal window; By using the following command structure: (Makes life easier!)

1. $ sudo su // su to root user.
2. $ {Enter your password next for the logged in user, you are trying to sudo!)
3. You should be as root user now. From here just drop the "sudo" before any commandline 
   script and run in the terminal or console without having to enter the password everytime you want to execute code lines.
# As easy as:
4. $ add-apt-repository "deb http://ppa.launchpad.net/nemh/systemback/ubuntu xenial main"