You can either create this file after booting into Red Hat Enterprise Linux or use the editor built into the EFI shell. To use the EFI shell, at the Shell> prompt, change devices to the system partition (mounted as /boot/efi in Linux). For example, if fs0 is the system boot partition, type fs0: at the EFI Shell prompt. Type ls to make sure you are in the correct partition. Then type edit startup.nsh. Type the contents of the file and save it.
The next time the system boots, EFI detects the startup.nsh file and use it to boot the system. To stop EFI from loading the file, type Ctrl-c . This aborts the process, and returns you to the EFI shell prompt.