UPDATE: Apple has just released iOS 8.0.2 to fix the problem affecting iPhone 6 and iPhone 6 Plus users. To update, go to Settings > General > Software Updates.
Shortly after the release of the iPhone 6 and iPhone 6 Plus, Apple has rolled out a new iOS 8.0.1 software update that was supposed to iron out some minor kinks. Unfortunately the little update was reported to be creating more problems, affecting its cellular service and TouchID Fingerprint scanner. It seems that it only affects iPhone 6 and iPhone 6 Plus that were updated to iOS 8.0.1.
Apple has responded that a fix is on its way in yet another update (iOS 8.0.2) but it would take a couple of days to release it. So for those who are affected, you can restore your iPhone 6 to proper working order by downgrading to iOS 8.0. Head after the break for the official instructions.
1. Make sure that you’re using the latest version of iTunes.
2. Connect your iPhone to iTunes.
3. Back up your iPhone in iTunes on your Mac or PC.
iCloud backups won’t restore to earlier versions, including iOS 8.0.
5. Select the file you just downloaded by doing one of these in iTunes:
Mac: Press the Option key and click Check for Update.
Windows: Press the Shift key and click Check for Update.
6. Press Update to install iOS 8 on your iPhone.
Take note that after reverting back to iOS 8.0, the health app will not work until its newer iOS 8.0.2 is released. These steps aim to bring your iPhone 6 back to acceptable working condition, especially vital cellular service.