Ok, changing the UUID is maybe not the best idea.
When you mount your hdd like at this steps decribed,
and then do the grub-install command from above again?
https://forum.manjaro.org/t/howto-chroot-from-or-into-any-linux-distribution/34071
&
https://wiki.manjaro.org/index.php?title=GRUB/Restore_the_GRUB_Bootloader