I did it in the past, it's easy:
myBackBarButton = [[UIBarButtonItem alloc] initWithImage:barButtonImage
style:UIBarButtonItemStylePlain
target:myWebView
action:@selector(goBack)];
myForwardButtom = [[UIBarButtonItem alloc] initWithImage:anotherBarButtonImage
style:UIBarButtonItemStylePlain
target:myWebView
action:@selector(goForward)];
Where myWebView is your UIWebView (In case it's your class, use self)
If your buttons are already created, then just add the target and the action to them:
myBackButton.target = myWebView;
myBackButton.action = @selector(goBack);
What you are doing is adding the action goForward: and goBack: of the target that is your webview, to those buttons.