Windows 10 saves a list of Wi-Fi networks you connect to along with their passphrases and other settings. If you want to stop your PC from connecting to a network automatically, you’ll need to make Windows “forget” the Wi-Fi network.
The process was obvious in Windows 7, where you could just select “Manage Wireless Networks” in the Control Panel’s Network and Sharing Center and delete saved networks. Windows 8 removed this option and forced you to use Command Prompt commands. But in Windows 10, Microsoft once again provides a graphical interface for this.