On June 8th, Apple announced that with Xcode 7, everyone would be able to install any apps they develop on their devices without an Apple Developer Program Certificate. The
If you've previously enrolled in the Safari Developer Program you may find yourself to be an 'Agent' (see your account in Xcode preferences to verify this).
Try logging in with another account, never used for development - create one if you must. Then you will appear as 'Free' and you will be able to fix all issues and finally install your app to your iOS Device.
First Of All, you must have a valid Apple Developer Account. But no need to add device UDID in developer a/c for install the app on the device. Follow below steps achieve above:
1) Install Xcode 7
2) Give a unique bundle identifier(Any unique identifier)
3) Select a valid team from "Team" option. (You can add account from Xcode preferences or there is an option for adding account)
4)Then Click on fix issue. It will take some time and will be resolved. (If you are getting any error, then there may be some issue with your Apple developer a/c).
5)If you are not getting any kind of error after Click on "Fix issue", then your set up is success.
6) Now connect your device. Run your Code on Xcode 7 by selecting the destination as your connected device name.
Hopefully it works for all. I have tried in Xcode 7 beta version. Good Luck and Enjoy....