well you just need to use a text editor in superuser mode like so:
you can then add the lines you need to the grub file
# note: if pico isnt there, try nano, or mcedit, or if you are in x you can use gedit, or kwrite.
basically you will add a line like this kinda you will have to match it for yousystem but...
title=Ubuntu (kernel version if you want)
kernel /(bzimage) root=/dev/hda5
now you will name the "(bzimage)" what your kernel image name is for example mine is vmlinuz-18.104.22.168. i dont use grub though but anyway that is what i would put there. your image should be in /boot of your partition. if you have a seperate boot partition and would like to use it then you will have to make that adjustment.
and notice the root line... it is hd0,4 means /dev/hda5 i know but makes sence if you man grub..
then just save it with pico you would hit crtl+o then crtl+x to exit it
then run grub...
reboot and it should all be there..
if this is all jibberish then post your /boot/grub/grub.conf file and ill try to help you..