this one helps. Since iOS 10, it's not possible to open the Settings app from a third party app. The only settings that are allowed to be opened are Keyboard setting but only by a custom keyboard extension and your own application settings. More details: here Note: Even for iOS 9, using the URL string that is mentioned in the question can lead to app rejection as it violates iOS App Review Guidelines.
My app rejected because uses the "prefs:root=" non-public URL scheme