Note: This guide is from inside a running OS, not for recovering a broken OS.
UEFI:
sudo rm /etc/grub.d/* -R sudo rm /etc/sysconfig/grub yum reinstall -y grub2-efi shim grub2-tools grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg
MBR/BIOS:
sudo rm /boot/grub2/grub.cfg sudo rm /etc/grub.d/* -R sudo rm /etc/sysconfig/grub yum reinstall -y grub2-tools grub2-mkconfig -o /boot/grub2/grub.cfg grub2-install /dev/sda