RHEL 7.5 boortloader error grub error

Hi all,
for some reason I used the disk utility on rhel 7.5 to change the partition type of a usb,
next boot I found that my boot partition has been deleted and the system was not able to boot,

a grub error

I used the installation media to enter the rescue mood trying to setup the boot partition again,

I typed the following commands
ls /dev/sd*
ls /sbin | grep grub2
/sbin/grub2-install /dev/sda

and got the following error

error: /usr/lib/grub/i386-pc/modinfo.sh does not exist. please specify --target or --directory.

please some one can help with that
I googled it several times but couldn't find a solution

Thank you
Hammam