Водопад сюжетный питон?

Попробуйте вот так: -

NSArray *viewControllerArr = [self.navigationController viewControllers];
// get index of the previous ViewContoller
long previousViewControllerIndex = [viewControllerArr indexOfObject:self] - 1;
UIViewController *previous;
if (previousViewControllerIndex >= 0) {
    previous = [viewControllerArr objectAtIndex:previousViewControllerIndex];
    previous.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc]
                                                 initWithTitle:@"Back"
                                                 style:UIBarButtonItemStylePlain
                                                 target:self
                                                 action:nil];
}