ViewControllerB.swift

@IBAction func handleLoginAction(_ sender: Any) {
        /*
         * This example is when we want to pop all view controllers from navigation backstack
         * & add a new view controller as the root view controller to the stack
         */
      
      /*  Step 1: Instantiate the new View controller. In this case: ViewControllerC */
      let storyBoard : UIStoryboard = UIStoryboard(name: "Main", bundle:nil)
      let viewControllerC = storyBoard.instantiateViewControllerWithIdentifier("ViewControllerC") as! ViewControllerC
      
      /*  Step 2: Get the list of view controllers from the navigationController */        
        var vcArray = self.navigationController?.viewControllers
      
      /*  Step 3: Remove all the view controllers from the stack i.e. ViewControllerA & ViewControllerB */      
        vcArray!.removeAll()
      
      /*  Step 4: Append the new view controller to the navigation stack */            
        vcArray!.append(viewControllerC)
        
      /*  Step 5: Set the stack of view controllers to the navigationController */            
        self.navigationController?.setViewControllers(vcArray!, animated: true)
    }