@pujithadimuthu This is current to the best of my ability:
In that Ubuntu doc the “Graphical way” and “Ubuntu Alternate CD” probably will not work in OM Lx. The section on “The terminal way” has elements needed but I think is not quite accurate for OM Lx.
OpenMandriva needs better documentation on this. And we will have that some day, but I won’t promise any time frame since everyone involved with OM Lx is an unpaid volunteer and we all have other work/family/life commitments.
However with this article you should be able to figure out how to do this on a Windows/OM Lx multi-boot system. I suggest using the Rescatux CD if it will boot for you as that can re-install grub2 automatically. If Rescatux does not boot you should be able to use Super Grub2Disk to boot in to your system and re-install grub2 with these commands. The first command creates the grub2 menu:
$ sudo grub2-mkconfig -o /boot/grub2/grub.cfg
Then this command installs grub2 to BIOS mbr or EFI Firmware:
$ sudo grub2-install /dev/xxx
where you replace the “xxx” with the name of the drive you want to, or were booting OM Lx from, like sda or if it is a nvme drive something like nvme0n1.
I do know that in normal circumstances, (meaning nothing was erased from /boot/efi partition that should not have been), then if user can use Super Grub2Disk to boot in to the system user wants to boot from the above commands do work to do that. (This has been tested.)
Also the above commands should include your Windows system in the grub2 menu.