It's easy enough. You just need a running Linux system with the same architecture. You need to be root in this system or to use sudo. Mount your Manjaro root partition on some suitable mountpoint.
Code:
sudo mount /dev/sda1 -t ext4 /mnt
It might not be sda1 of course. Use the correct partition and filesystem type for your system.
To actually chroot,
That will make the root partition of the Manjaro system your new root partition. All the software you use from then onward is Manjaro software. Only the kernel still belongs to your host system.
When you are finished, just type "exit" to get back to the host.