You can make the phone forget about the details of a Wi-Fi network that you added. For example, if you don’t want the phone to connect to it automatically or if it’s a network that you no longer use.
Turn on Wi-Fi, if it’s not already on, then tap Wi-Fi in the Settings menu.
In the Wi-Fi settings screen, touch and hold the name of the network that you want to forget.
Tap Forget network in the Context menu that appears.