Apple said it would release iOS 8.0.2 in the next few days to fix the issue. In the meantime, it offered step-by-step instructions to reinstall iOS 8 using iTunes.                

The company said users should make sure that they are using the latest version of iTunes before reinstalling iOS 8.
Apple said its health app would not work in iOS 8 after these steps, but would be fixed in iOS 8.0.2.
The company pulled the iOS 8 system after users took to microblogging site Twitter to post their complaints.

Apple announced that it was investigating the reports and would issue advice to users "as quickly as we can." Users are still able to the upgrade older phones to last week's version of iOS 8, which Apple said has already been downloaded to nearly half of all iOS devices.
Some tech blogs reported the update only seemed to cause problems for the latest phone models -- the new iPhone 6 and 6 Plus. It's not uncommon for new software to contain bugs that have to be fixed with subsequent releases.