When updating the firmware, we require the user to physically press and hold a key in order for the Firmware to be loaded.
This is for security reasons.
The update process is designed so that it will never be triggered accidentally. This way, it is also impossible for malware to enter, thus making the keyboard impenetrable for unwanted firmware.
Once you click "Start Countdown" in the Firmware Update Process, the countdown begins and as soon as the keyboard lights turn off, you would need to instantly press and hold the key on the top left corner of your Raise (usually the Esc key).
You can release the key once you see the message: "Firmware flashed successfully!"
More information: How do I update my keyboard's Firmware?