How can I connect new iphone7 to WiFi

On the phone select the network you are trying to connect to and then "Forget This Network."

Turn off the router.

On the phone reset network settings and then turn the router on again and see if it connects.

If not, reset the router to factory settings and on the phone reset all settings and try again.

If you have a dual-band router try the other band.

Finally, check if there is a firmware update for the router.

If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network - Apple Support

Assuming you have went to Settings>Wi-Fi, selected the network and added the password, it should work. If not, I would try a different network, even at another location and see if you can connect to it. If so, the problem should be an entry error. Not hard to do on the phones because of the keyboard size.