Get reference to View ControllerA from ViewControllerB to change property

I have a custom ViewController A with an instance variable or property that I want to change from a second custom view controller launched by a navigation controller for ViewControllerA.

Here is my code to launch ViewController B from within A

In FirstCustomVC:

- (void) launchSecondVC {
    UIStoryboard *storyBoard = self.storyboard;
  
    CustomVC * myVC =
    [storyBoard instantiateViewControllerWithIdentifier:@"myvc"];
    UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController: CustomVC;
    [self presentViewController:nav animated:YES completion:nil];
}  

After ViewController B is launched and the user does something, I want to dismiss ViewController B and enable a button back in ViewController A. I can dismiss VCB but I am having trouble grabbing a reference to A in order to enable the button.

The following successfully dismisses VCB. However, the presenting ViewController is a navigation controller and does not have the property I need so it crashes if I try to access the property.

[self.presentingViewController dismissViewControllerAnimated:YES completion:nil];//dismisses successfully
self.presentingViewController.myButton.enabled = YES;//crashes as the property is on the VC, not the nav

I've tried various methods to get the topViewController but can only get a generic UIViewController rather than the custom one with the button property.

How can I grab a reference to the custom VC that is actually displayed on the screen?

The best option is using delegation. It prevents tight coupling between controllers and ensures clean, modular, and reusable code.

CustomVC.h:

@protocol CustomVCDelegate <NSObject>
- (void)customVCDidFinish:(BOOL)enableButton;
@end


@interface CustomVC : UIViewController
@property (nonatomic, weak) id<CustomVCDelegate> delegate;
@end

FirstCustomVC.h:

#import "CustomVC.h"

@interface FirstCustomVC : UIViewController <CustomVCDelegate>
@property (weak, nonatomic) IBOutlet UIButton *myButton;
@end

FirstCustomVC.m:

- (void)customVCDidFinish:(BOOL)enableButton {
    self.myButton.enabled = enableButton;
}

- (void)launchSecondVC {
    UIStoryboard *storyBoard = self.storyboard;
    CustomVC *myVC = [storyBoard instantiateViewControllerWithIdentifier:@"myvc"];
    
    myVC.delegate = self; // Назначаем делегата
    
    UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:myVC];
    [self presentViewController:nav animated:YES completion:nil];
}

CustomVC.m:

- (void)dismissAndSendData {
    if ([self.delegate respondsToSelector:@selector(customVCDidFinish:)]) {
        [self.delegate customVCDidFinish:YES]; // Сообщаем делегату включить кнопку
    }
    
    [self dismissViewControllerAnimated:YES completion:nil]; // Закрываем ViewController B
}