Q: WIFI discovery problem

Hello kimsong17,

Thanks for reaching out to the Apple Support Community. I know how important it is to be able to rely on your Wi-Fi working as expected, especially if cellular data is not you preferred connection. I have some steps that may help you re-establish your connection.

With the behavior you've described, being unable to connect to multiple networks it may be a good idea to reset the network settings in your iPhone. This will not delete any info form your phone but will require you to re-enter your Wi-Fi passwords. 

To reset the network settings you can go to Setting > General > Reset > Reset Network Settings. 

Your phone will reboot after a moment. Try to reconnect to your Wi-Fi under Settings > Wi-Fi, and if you have any more trouble, the entire community is here to help.

Best Regards