IPhone : How to call a XIB and return to the calling XIB?

I have an app with two (2) XIB files; one is the main view, the other is a help view. I have view controllers created for both. I have a button on the main view XIB that calls the help view which works like this:

- (IBAction)bDisplayHelp:(UIButton *)sender {

HelpViewController *svc = [HelpViewController new];
svc = [[HelpViewController alloc] initWithNibName:@"HelpViewController" bundle:nil];

[self.view addSubview: svc.view];

}

On the Help view, I have a button which I want to take the user back to the Main view. This is my code (which is not working):

- (IBAction)bBackToMainNib:(UIButton *)sender {

MainViewController *tvc = [MainViewController new];
tvc = [[MainViewController alloc] initWithNibName:@"MainViewController" bundle:nil];
[self.view addSubview: tvc.view];

}

All I did was essentially go back and forth. I'm getting this error at runtime when I attempt to return to the Main view (doesn't execute the first statement, just crashes):

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFString bBackToMainNib:]: unrecognized selector sent to instance 0x7d3586b0'

What am I doing wrong?