Boot a live media - preferably the same edition - mount your root partition on the temporary /mnt mountpoint e.g. sdy is an example - you will need to adjust for your system
sudo mount /dev/sdy2 /mnt
If your system is EFI then mount the efi partition
sudo mount /dev/sdy1 /mnt/boot/efi
In the topic [root tip] [How To] Do a manual Manjaro installation follow the instructions to reinstall the list of packages which made up the initial installation.
There may be other steps needed but that should get you started.
You got to love this quote
Unix was not designed to stop its users from doing stupid things, as that would also stop them from doing clever things.
— Doug Gwyn