How to boot server with older kernel and set it as default in CentOS and AlmaLinux

Identify the Linux Kernel installed on your server by executing following command in shell on file /boot/grub/grub.conf;

grep '^[[:space:]]*kernel' /boot/grub/grub.conf

To boot from old kernel which is 0 in /boot/grub/grub.conf, change the default value of old kernel to 1 in /boot/grub/grub.conf.