All default 'Apple' icons disappeared on iPhone 7
As long as you know the AppleID and password for the device, you can restore without needing to get to the settings app:


https://support.apple.com/en-us/HT201263


This option is needed for service and if you sell a device and forget to unlock it before it leaves your possession. When multiple apps are broken, a restore is almost always the fix and something you should try once you back up the device as best you can before the erase.