When you Hold your finger on lower bottom left part of LCD screen and when you connect zumo to Pc you must still hold screen and quick press and hold power button
When you see in updater window that your unit is recognized release finger from power button but still hold screen and click on OK button in updater.
You can also try this.
Connect unit to Pc and when you see logo quick press finger on lower left corner of screen and press power button with other hand.
p.s.
If you have some older FW on your unit you can also try with this:
- Open battery cover
- add some small magnet beside usb hole on your unit ( this will simulate closed battery door ) Yo can use small magnet for sticker on the fridge
- now folow tutorial from dasilvarsa