my iPhone 7 is restarting

Assuming you are on iOS 11 on your iPhone 7. All iOS versions except iOS 11.2 has the phone restart bug issue. Update to iOS 11.2 and there will be more more automatic restarts. Also ensure you are good signal coverage during the update process as iPhones (with iOS 11) tend to go into a restart loop if there is insufficient network coverage.

Basic troubleshooting from the manual are restart, reset, restore from backup, restore as new.