Pop 2 view controllers in Nav Controller in Swift

Expanding on my comment, find the second last view controller in the viewControllers array and then use popToViewController to avoid overwriting the entire view controller stack.

Example (assumes the navigation controller has more than 1 view controller):

func backTwo() {
    let viewControllers: [UIViewController] = self.navigationController!.viewControllers as [UIViewController]
    self.navigationController!.popToViewController(viewControllers[viewControllers.count - 3], animated: true)
}

Objective-C

NSArray *viewControllers = [self.navigationController viewControllers];
[self.navigationController popToViewController:viewControllers[viewControllers.count - 3] animated:YES];

I wrote an UIViewController extension (Swift 3+ ready)

You could use like this :

/// pop back n viewcontroller
func popBack(_ nb: Int) {
    if let viewControllers: [UIViewController] = self.navigationController?.viewControllers {
        guard viewControllers.count < nb else {
            self.navigationController?.popToViewController(viewControllers[viewControllers.count - nb], animated: true)
            return
        }
    }
}

Usage :

self.popBack(3)

Bonus dismiss to a specific viewcontroller

/// pop back to specific viewcontroller
func popBack<T: UIViewController>(toControllerType: T.Type) {
    if var viewControllers: [UIViewController] = self.navigationController?.viewControllers {
        viewControllers = viewControllers.reversed()
        for currentViewController in viewControllers {
            if currentViewController .isKind(of: toControllerType) {
                self.navigationController?.popToViewController(currentViewController, animated: true)
                break
            }
        }
    }
}

Usage :

self.popBack(toControllerType: MyViewController.self)