CluelessPerson: you should locate your iso first by doing this
ls
ls (hdX,Y)
for example :
ls (hd0,1)

now to the main linux partition..
assuming it is: hd0,1

assuming your installed linux partition is hd0,1
assuming your iso lives in hd1,1
type this :

set prefix=(hd0,1)/boot/grub

insmod linux
insmod loopback
insmod iso9660
insmod fat
insmod ntfs
insmod nftscomp


loopback loop (hd1,1)/<path to ISO>/<ISO-name.iso>

set root=(loop)
linux /casper/vmlinuz boot=casper iso-scan/filename=/<ISO-name.iso> noprompt noeject
initrd /casper/initrd.lz

boot

---------

if it boots,

sudo blkid

assuming it is /dev/sda:

sudo grub-install --boot-directory=/mnt/boot /dev/sda

sudo update-grub