Solution:
1. Mi TV & Mi Box will automatically connect to the previous WiFi network after boot/restart.
2. If you want to modify the default WiFi of automatic connection, it is suggested to refer to the following train of thought:
① Open "Settings" -- "Network" -- "Wireless Network" -- select the name of the connected WiFi, and then press the OK button of the remote control. In the interface that appears, select "Ignore this network";
② Then manually connect to the new WiFi. The new WiFi network will be connected by default after the next boot or restart.