I don't know whether my procedure was a right one or not. In order to see the iMeter_xxxxxxxx AP, the iMeter must run in the AP Mode.
I logged in using the Local button (red) on iMeter APP and removed the wifi password. The iMeter then restarted and entered its AP Mode because it couldn't connect to the home AP.
iMeter_xxxxxxxx is available for firmware update. Then put the wifi password back. :)
The local mode can be visited by
1 if the energy meter is in AP mode, your phone needs to connect the ap of iMeter_sn.
2 if the energy meter is connected to the router successfully, the app will visit the local IP(it will find the IP of the energy meter by ssdp).
This process is equal to visiting the HTTP://126.96.36.199 or your local IP by a browser, which is no need to input the password.
The password is only used when you log into your account of IAMMETER-cloud.