Resetting unknown E-Tube Passkey
You can reset the Wireless passkey - even if you don't know the current one - by connecting your bike to a windows computer/laptop using the charger.

Download e-tube for windows at https://e-tubeproject.shimano.com

Then do this:


Connect the bike to your computer using the charger and Junction A
Open the e-Tube windows app
Make a connection by clicking "connection check"
Click "Bluetooth LE settings"
Set a new passkey


You can now use the passkey you just set to connect to your bike using BluetoothLE/ANT+. The Passkey is required for wireless connections only.

Also: if you really want to update firmware then I recommend using a computer (over USB) rather than the mobile app. It a bit safer. You can update using the mobile app, of course.. but as far as I'm concerned the mobile app's main feature is changing settings easily (out on the road).

More info: 


resetting your passkey: https://di2center.com/2019/05/05/change-your-di2-wireless-passkey-using-the-e-tube-app-or-windows-computer/  (2nd half of page) 
connecting to computer https://di2center.com/2019/04/22/how-to-connect-your-di2-system-to-your-computer/


(disclaimer: my website ;). If you're having more problems and can't figure things out don't hesitate to ask)