How to restore your iPhone 7 / 7 Plus with iTunes by entering Recovery Mode. This is the same as a hard reset but via iTunes.
1. If you have iTunes, then make sure you have the latest version. If you do not have iTunes, then download it from apple.com/iTunes
2. Open iTunes on the computer and leave it running
3. Power off your phone. You can try soft resetting it with the Power + Volume down button for about 5 seconds and it should turn the phone off
4. Plug the lightning cable into the phone but do not plug it to the computer yet
5. You will plug the lightning cable into the phone and immediately press and hold the Power button + Volume Down button
6. When you see the apple logo, release the power button but still keep holding the Volume Down button
7. Release Volume Down button when you see the connect to iTunes on the display of your phone
8. On iTunes press Restore
9. then click on Restore and Update, Next and Agree to the terms and conditions
10. The download is 2.4+GB so the download can take some time but once iOS10 is downloaded to the computer, then you can click on Restore iPhone.
11. Follow the remaining prompts and it will ask you to setup your iPhone after completed.
Reminder! Restoring your iPhone erases everything so if you do not have a backup of your data, it will be deleted.