how to backup my iphone 7 if screen is unresponsive

If you can’t get into your phone, you will not be able to back it up. If you had it set up for a daily iCloud backup and if it was connected to your WiFi network before you had this screen problem, you should still get an iCloud backup. You will need to get your screen fixed.

Not with iCloud you can’t. There is a chance that you could backup with iTunes, if you had done so in the past and already trusted the computer and had the correct settings for connecting USB devices, but I’m guessing you’ve never backed up with iTunes before or you would not be asking.

Did you try the suggestions in the related article in the upper left corner of this web page?