I’m assuming you have a “normal” install on an EFI system? Do you have /boot and /boot/efi partitions (check your /etc/fstab)?
If so, the command is $ sudo grub2-mkconfig -o /etc/grub2-efi.cfg
Edit:
Nevermind then.
Double edit:
I think the OP was supposed to edit the plain text file, not generate it using grub2-mkconfig. I’m afraid the generated file might now be gobbledygook.