To access that root shell, follow these steps:

Reboot the system.

• Interrupt the boot-loader countdown by pressing any key, except Enter.
• Move the cursor to the rescue kernel entry to boot (the entry with the rescue word in its name).
• Press e to edit the selected entry.
• Move the cursor to the kernel command line (the line that starts with linux).
• Append rd.break. With that option, the system breaks just before the system hands control from the initramfs image to the actual system.
• Press Ctrl+x to boot with the changes.
• Press Enter to perform maintenance when prompted.

To reset password you need to:

• Remount /sysroot as read/write.

  mount -o remount,rw /sysroot 

• Switch into a chroot jail, where /sysroot is treated as the root of the file-system tree.

  chroot /sysroot 

• Set a new root password.

   passwd root 

• Ensure that all unlabeled files, including /etc/shadow at this point, get relabeled during boot.

   touch ./autorelabel 

• type exit twice

this can take a while other option is to use

load_policy -i

this causes Selinux policy to be loaded and now we can use Selinux commands

 restorerecon -FvR /etc/shadow

This relabels /etc/shadow correctly. You can exit the server and reboot as it will start to generate errors

when making changes to grub you need to edit the /etc/default/grub once you are done you need to regenerate the grub config file

 grub2-mkconfig -o /boot/grub2/grub.cfg