Every Ubuntushop  Manjaro computer has a Manjaro Live Boot Option , for, if needed, start a live session or reinstall Manjaro.(video boot to live manjaro)  (video reinstall)

If you want to reinstall, backup your /home/username folder to a usb stick or cloud.

Start Manjaro and search in  menu  "man" and press menu-item  manjaro-live

Provide your password and hit ok

Select your Manjaro taste and hit ok:

The latest version will be downloaded and after that the computer will reboot in the manjaro version live.

After reboot, you will have a live version of Manjaro loaded in ram. You can test it or install a fresh manjaro . The installer will start once you hit the manjaro-install desktop shortcut.(warning!: if you reinstall manjaro, all data will be erased)

Enjoy.