Forget Wi-Fi on Phone/Tablet
Turn on Wi-Fi, if it's not already on.
Click on Wi-Fi
Find the network you want to get rid of
Long press it, then choose 'Forget'
To forget a Wi-Fi network on TV
From the Home screen, tap Apps > Settings > Wi-Fi.
In the Wi-Fi settings screen, tap and hold the name of the network that you want to forget.
Tap Forget network in the Context menu that appears.
How to forget wireless networks on the Laptop
Click the Wi-Fi Network icon on the lower right corner of your screen.
Right click on the network name you want to clear on the list.
Select 'Forget'