Apart from edit /boot/grub2/grub.cfg or /etc/grub2.cfg. We’d better use grubby to config grub.
Here is the example of how to select default grub.
If grub missing due to anyreason, and you are fall back to grub menu, you can try
As the kernel version is not the same, you can use TAB to find and complete the name
Reference: Grub menu missing Linux Kernel entries
For RHEL8, the loader entry is under
/boot/loader/entries/ and the bootup option is in
Author Hangbin Liu
LastMod 2019-03-20 (cad1651)