Execute chroot command to access your filesystem.
chroot /mnt/sysimage
By using grub2-mkconfig command, you can regenerate grub.cfg file.
grub2-mkconfig -o /boot/grub2/grub.cfg
If you are working on an UEFI based machine then you have to generate grub.cfg file in /boot/efi/EFI/centos/ directory.
If you are using SELinux, then create following file to trigger SELinux file relabeling process on next startup.
touch /.autorelabel
Finally exit from chrooted environment and reboot your system.
bash-4.4# exit
sh-4.4# reboot
