Generally the parent view controller is responsible for dismissing the modally presented view controller (your popup). In Objective-C you would do something like this in the parent view controller:
[self dismissViewControllerAnimated:YES completion:nil];
The same code in Swift versions < 3 would be:
self.dismissViewControllerAnimated(true, completion: nil)
Swift 3.0:
self.dismiss(animated: true, completion: nil)