How do I reset my preferences?

Make a full backup of your system. Turn off Wi-Fi. You need to copy five files related to network preferences to a removable drive, so you can restore them if necessary. In Finder, browse to the top of your Mac’s startup disk and then dig into /Library/Preferences/SystemConfiguration. Move (as opposed to copy) the following files to your removable drive, then eject that drive:

com.apple.airport.preferences.plist com.apple.network.eapolclient.configuration.plist com.apple.wifi.message-tracer.plist NetworkInterfaces.plist preferences.plist

Restart your Mac and turn on Wi-Fi again; macOS will recreate those files, which should no longer include any problems that existed in the versions you removed.