Assuming bios-legacy and no separate /boot partition.
Start your KaOS install media (or from any grub menu) and when you come to the install menu, press 'c' to go to the grub prompt (grub> )
Do not boot up to live OS, but press ‘c’ at the menu and we’ll see grub> .
grub> search.file /etc/KaOS-release root
grub> probe -u $root --set=abc
grub> linux /boot/vmlinuz-linux root=UUID=$abc rw
grub> initrd /boot/initramfs-linux.img
grub> boot
When booted, check uuid's of fstab with blikd.
If correct or after correction, at terminal
sudo grub-install /dev/sda
sudo update-grub