Asus FX504 BIOS boot issue

I recently bought an Asus FX504 laptop which I wanted to upgrade the HDD + Intel Optane with my SSD.

After removing both the hardware above and installing my SSD, I am entering the BIOS each time I turn on the laptop.

The SSD has an OS already from a previous laptop, and I also have a bootable USB pen with Windows 10 files so I can reinstall a fresh copy of Windows.

I have read people having the same struggle but I don't seem to find a solution.

Things I have tried/to be considered:

• Disabled Secure Boot and Fast Boot however I am still unable to either boot from my HD or USB pen. (Unable to locate an option for CSM in "Boot" menu which I read should be enabled.)

• The Boot menu is empty so I am seemingly unable to change the boot order.

• Removed CMOS battery for a minute.

• USB pen is fine as its being detected and bootable by another laptop.

• Both SSD and USB is being detected in the BIOS main screen.

This is driving me mad! Any help is much appreciated.
(Pictures to follow I hope

Goal: Boot from USB drive to re-install Windows.

Setup:
Laptop: Asus FX504GD-E4673T
BIOS: American Megatrends 312
EXISTING Hard Drive: HHD + Intel Optane
NEW Hard Drive: Samsung 850 EVO

BIOS images: https://imgur.com/a/GuO7niq