B4R Question Reset WeMos D1 R2 to factory firmware?

While testing some stuff out, I flashed one of my Wemos D1 R2 boards with some non-factory firmware & now I'd like to get it back to how it was before. I tried this tutorial -> https://wiki.wemos.cc/tutorials:get_started:revert_to_at_firmware, however it doesn't seem to have worked as I get the following error in the log window of the ESPFlashDownloadTool:

CONNECT BAUD: 115200
============
.Uploading stub...
Running stub...
Stub running...
Changing baud rate to 1152000
Changed.
-----------------------
crc_efuse_4bit: 0
crc_calc_4bit: 11
48bit mac
Traceback (most recent call last):
File "EspDownloadFrame.pyo", line 74, in OnNotebook1NotebookPageChanged
AttributeError: 'wxPanelGrid' object has no attribute 'fm1'

Click to expand...

Does anyone have a reliable way of getting a D1 R2 back to factory firmware?

Thanks - Colin.