Hello.
Solution to do a Factory Reset without the App (example : smartphone is lost, no more access to the App).
I spent time to understand, the key information: you can use a new installed App, despite this new installed App has not been previously linked to the device.
Thus install the App, and then follow the regular process: Menu > Help > factory reset
This will do the connection to the device to reset. Despite this is a new App, it works, Yeaah!