iPhone or iPad
1. Go to Settings > Wi-Fi.
2. Tap "i" button next to the Wi-Fi network that you want your device to forget.
3. Tap Forget This Network, then tap Forget to confirm.
Mac
1. Choose Apple menu > System Preferences, then click Network.
2. Select Wi-Fi in the list on the left.
1. Click the Advanced button.
2. The Wi-Fi pane shows a Preferred Networks list. Select the Wi-Fi network that you want your Mac to forget.
Windows
1. Type Settings on the search box.
2. Click Network & Internet.
3. Click Wi-Fi on the left pane of the Network & Internet window.
4. Click Manage Wi-Fi settings.
5. Select the network name and click Forget.
Android
1. Open Settings on your device, and tap on the WiFI icon to access WiFi network options.
2. Tap and hold the WiFi network you want to delete, then select Forget Network from the menu that appears.
Chromebook
1. Sign in to your Chromebook.
2. At the bottom right, select the time.
3. Select Settings
4. In the "Network" section, select Wi-Fi.
5. Select Known networks.
6. Find the network you want to forget, then select More 
Forget.