override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
//if destination is VC1 OR VC2...

    if let destVC = segue.destination as?
    FavouriteDetailViewController || FavouriteExerciseDetailViewController

//... then pass the values as specified

    destVC.favouriteWorkoutPassed = workoutToPass
    destVC.favouriteObjectPassed = favouriteObjectToPass
    }