If your device is blocked during the upgrading procedure, please follow the steps below:
Charge your device
Go to the application then click on the settings menu
Make sure that the device is not paired with the phone (You must see a "unpair instead of pair" section).
Then, click on Help section and select the sub-section Fix firmware upgrade issue
Select the visual corresponding to the icon that appears on your watch (upgrading icon)
Click on the search icon, select your device and click repair
This procedure should repair your device and fix this issue.
Then, perform a new upgrading procedure.