Freecom Silverstore-2 2-bay 'Nas' has a System fault (no replies)

Hi all,
I am new here, just registered.

I have an old Freecom Silverstore-2 'Nas' which is bought second hand from the internet.
Unfortunately the device won't boot.

When I power it up then within 10 seconds the Activity Led becomes red, meaning System fault.
I can get a direct connection from my Laptop to the device using a network cable, but nothing more than that.

Searching the internet I found on this forum a topic from 2018 about that device (https://forum.doozan.com/read.php?2,68094).
I have read the posts, but I don't understand everything; not familiar with all posted.

However, I would like to try to flash new firmware to my device, if it's possible.

I have read it could be done using an UART-USB device.
I have bought such an UART device (with a FTDI chip) and I used it once, flashing OpenWrt on a bricked network drive.

I have seen a picture of the motherboard of the Freecom, having a serial port.

I tried to dismantle the device; removed the screws on the back, but I can't get the board out of it. It looks like it get stuck somewhere, can't see it.

Could somebody please tell me how to get the board out?
Perhaps showing some pictures?

Thank you in advance.