Here is a possible solution to your problem, let me know if it works for you.
Mount the disk to another instance, see link 
Update grub.cfg to use the previous kernel version.
Note : make sure you are changing the correct grub.cfg file. If there are linuxefi and/or initrdefi entries in the grub.cfg file, then it most probably uses the /etc/grub2-efi.cfg file that points to /boot/efi/EFI/redhat/grub.cfg, instead of /etc/grub2.cfg that points to /boot/grub2/grub.cfg.
Attach the disk to the faulty instance, see link
The instance is able to boot
Reinstall the kernel
Reboot the instance
I'm curious to see if this worked in your case, have a nice day.
from : Derek
 Detaching and reattaching boot disks :