Thank you for your answer.
Unfortunately it seems that I cannot do that.
When powering the Arduino on, the pwr led will shine, but double clicking the reset button not do anything. Perhaps have I missed something in this process ?
As I have explained, the Arduino is not seen in Device Manager, no COM port thus, and therefore it does not show up in Arduino IDE.
The only occurence I have it appearing is when booting it in DFU mode (boot & reset & boot release), it shows as DFU in FS mode. I have tried flashing the bootloader again, but still no progress.