Build permissions using Testflight
I have successfully created an IPA using Xcode 6.1 and uploaded to TestFlight, but whenever I tried to test, it shows the following screen, where should I change the build permission?
Right after you have uploaded the binary to the TestFlight it should show you the page with permissions e.g. the list of devices which you can test the app from your provisioning profile which you have used to sign the app. From that list you should check some of the devices, and click the "Update and Notify" or "Just Update" button. In your case, I think you have missed that step, and now you can go to TestFlight, navigate to your app, select the proper build, click permissions on the left, select the devices you want to permit to test your app, click the "Update and Notify" or "Just Update" button. Now you can test the app (if your device is on the list, of course)! Good Luck!