If you’ve used a public Wi-Fi network that requires you to sign in with your email or phone number, it’ll be added to your list of saved networks. If you’re worried about security, you can delete those networks to keep them from connecting automatically without your knowledge.
Here’s how to delete WiFi network on Android:
Open the Settings on your phone.
Tap on Network & Internet.
Tap on Wi-Fi.
Tap and hold on the Wi-Fi network name. This brings up a pop-up menu where you need to select Modify network.
Tap on the Advanced options drop down.
Check the box next to Forget network button. Tap Save button at the top right corner of the screen.