Boot from USB through grub menu

First, make sure you have secure boot disabled from the firmware settings. Once you are in the grub command line, type ls to list all partitions

grub>ls 
(hd0) (hd0,gpt1) (hd1) (hd1,gpt8) (cd0))

Type ls (cd0) to get the UUID of the device.

grub>ls (hd0,gpt1) 
Partition hd0,gpt1: Filesystem type fat - Label `CES_X64FREV`, UUID 4099-DBD9 Partition start-512 Sectors...

Note the UUID of your USB drive, shown in the above command

Type the following commands

insmod part_gpt
insmod fat
insmod search_fs_uuid
insmod chain
search --fs-uuid --set=root 409-DBD9

Replace the UUID of your device

Now we select the EFI file to boot from

chainloader /efi/boot/bootx64.efi
boot

That’s it; that should boot the USB drive.