Translations:GRUB/Restore the GRUB Bootloader/10/en
Use manjaro-chroot
Manjaro deploys a script called manjaro-chroot takes an optional argument which will search the visible devices - scan the partitions for signs of an operating system. If more than one Linux operating system is found you will get a choice of which system to chroot otherwise the file /etc/fstab from the system is used to mount the partitions and chroot into this system.
root # manjaro-chroot -a