The iOS 8.0.1 update was filled with bugs that broke Touch ID and cellular data for many iOS users of the iPhone 6 and iPhone 6 Plus features. If you face with such troubles or you just don’t like it, you need to downgrade to iOS 8.0. Here's the instruction on how to downgrade iOS 8.0.1  to iOS 8.0. Please follow these steps: 1.    Please don't forget to backup your iOS device to iCloud or using iTunes. So you will save your information and can recover your data from the backup if anything happened wrong. 2.    Connect the device running iOS 8.0.1  to your computer. 3.    Download the appropriate iOS 8 firmware (.ipsw) file for your device. 4.    Open the device page on iTunes, and hold the Option key (Shift for Windows users) while clicking the Check For Update button. Please note that it is important to hold the Alt/Option key or Shift key when you click on the Check for Update button directly, you will get an error message that iOS 8.0.1 is the current version. 5.    Find the IPSW firmware file that you downloaded in Step 1, select it, and click Open. 6.    iTunes will inform that it will erase and restore your iOS device to iOS 8 and will verify the restore with Apple. 7.    Click the Update button to proceed. 8.    iTunes should now downgrade your iOS device to iOS 8. 9.    Wait until your device updates, and enjoy your iOS 8.0 installation, with working Touch ID and cellular data! It is really useful method. Because you don’t lose any of your phone’s settings or data. All staff: pictures, music, messages, email, etc. should be ready and waiting for you till you downgrade iOS 8.0.1 to iOS 8.