You can’t easily alter the view hierarchy of a UIAlertView in iOS 7. (Nor should you; the documentation specifically tells you not to.) Head over to the developer forums to see a long discussion about it.
One alternative in your case is to set alert.alertViewStyle = UIAlertViewStylePlainTextInput;
This will add a text field for you. You can access it in the UIAlertView delegate callback by using UITextField *textField = [alertView textFieldAtIndex:0];
.