How do i set a @property of another class?

My interface is more complicated than this, but for simplicity, i’m going to describe is at this: I have 2 views.The app loads, the first view opens up and there is a textfield and a button. The user hits the button and brings them to the second view where there is another button and another textfield. What i want to do is have the user enter a value in the second view textfield, and when they hit the button to return to the first view, give the first views textfield the value that the second view textfield had.

So basically, i have the second views textfield stored in a variable called “actualAverage” and when the second view button is hit, this action fires:

- (IBAction)backButton:(id)sender {
    if (haveValueToReturn) {

        //set the firstviewtext box to the percent somehow
        FirstViewController *firstViewControllerObject = [self.storyboard instantiateInitialViewController];
        firstViewControllerObject.string = [[NSString alloc] initWithFormat:@"%f", actualAverage];
    }

    //switch the views
    [self dismissViewControllerAnimated:YES completion:nil];
}

Everything logically and syntactically appears OKAY, but when i run it, the value set to firstViewControllerObject.string is nil. Every time and i have no idea why… Any help would be very much appreciated