How do I "forget" an out-of-range Wi-Fi network on a Galaxy S7?
The method described in this answer does not require root, but it does require that you have a Wi-Fi access point ("router") you control.



One possible but very tedious and hacky solution is to host the SSIDs on a Wi-Fi access point you control, so that they are visible on the S7. Then you can "forget" them through the normal Wi-Fi settings page. The list of saved SSIDs can be retrieved (but not altered directly!) with third-party Wi-Fi management apps.

Having an access point capable of hosting "guest" networks/SSIDs is particularly helpful here. Otherwise, you'll need a wired connection so you don't kick yourself out by changing the SSID around.

Of course, this is quite a terrible solution in every way except that it works. So hopefully someone will have a better solution available.