At home I have two different WiFi networks, both known to all my mobile devices. One is our internal network, password protected. The other one is an open Freifunk network. It's nice to walk around in the village and automatically connect to other Freifunk WiFi routers, instead of using expensive mobile data.
But when at home I really want my devices connected to our internal network. Makes it easy to copy files between devices, or access services only available in our internal network. Plus the native WiFi connection is much faster than the Freifunk connection, which is limited by the speed of the VPN.
However Android connects to the last used WiFi network, and when the last one was another Freifunk router, it will connect to this network at home as well. By default, Android does not allow to prioritize networks. That's where "WiFi Prioritizer" comes to the rescue!
It's an Android app, available in the Play Store, and really easy to use. Just move known WiFi networks up and down, and whatever is on top will be used automatically - if available.
If several networks are available, and the Android device is currently not connected to the top one in the list (see screenshot), the app will disconnect from the current network and reconnect to the top one. All you have to do is re-shuffle your networks, and bring them in the correct order.