To flash or erase your NANOS3, you have to first put it into download mode.
NANOS3 doesn't include buttons for RESET and IO0, which should be provided by adding external buttons via a carrier board or other method.
To put the NANOS3 into download, follow these steps:

- Press and hold the [BOOT] button
- Press and release the [RESET] button
- Release the [BOOT] button

Now the board is in download mode and the native USB will have enumerated as a serial device.
