If your Xcode is showing "My Mac 64-bit” as your current device, then this is a/the problem. First see if your iOS Simulator is available in the dropdown list. If not, then your project file has changed, potentially corrupted. Close Xcode and re-open, if this doesn't fix it, then look within your Project settings, and change it so that the Project is for iOS (this may require trial and error).
Once that's fixed, if you keep getting CoreServices issues, make sure the CoreServices framework is imported in your project (check through Project settings).