Copying partition is straightforward. Made using gparted.
Create bootable USB stick (Startup disk creator in Linux mint), boot from it. Assume we have following partitions:
boot /sdb1 (don't really know how it works)
root /sdb2
home /sdb3
- Do
sudo mount /dev/sda2 /mnt
## if you have boot partition:
# sudo mount /dev/sda1 /mnt/boot
sudo grub-install --root-directory=/mnt /dev/sda