There is a few way you can do it. First is create DashboardViewController and present it to view hierarchy:
DashboardViewController *vc = [[DashboardViewController alloc] init];
[self presentViewController:vc animated:YES completion:nil];
Another one is create segue in storyboard from Login to Dashboard and when you want to redirect just call:
[self performSegueWithIdentifier:@"SEGUE_IDENTIFIRE" sender:nil];
SEGUE_IDENTIFIRE is a segue name you need to set up in storyboard.