macOS - How to Forget a WiFi Network

1. Click the Wi-Fi Network button at the top of the screen. 
2. Click the Wi-fi Settings... button. 
   
3. Click the Advanced... button at the bottom of the page.
   
4. Under Known Networks, click the . . . button to the right of the Wi-Fi Network you want to forget.
   
5. Click Forget This Network.
6. Click Remove.