问怎么去ViewController？

EN

if (!fileExists) {

UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Download audio?" message:@"" preferredStyle:UIAlertControllerStyleActionSheet];

UIAlertAction* actionAdd = [UIAlertAction actionWithTitle:@"Ok" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {

UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
        spinner.frame = CGRectMake(0, 0, 24, 24);
        UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
        cell.accessoryView = spinner;
        [spinner startAnimating];

        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

NSString *stringURL = @"https://drive.google.com/uc?export=download&id=0B6zMam2kAK39R2Z5RlVWZkN3Vzg";
                NSURL  *url = [NSURL URLWithString:stringURL];
                NSData *urlData = [NSData dataWithContentsOfURL:url];
                [urlData writeToFile:filePath atomically:YES];

        });
        if (fileExists) {
        [self performSegueWithIdentifier: @"detailSegue" sender: self];
          }  

    }];
    UIAlertAction* actionCancel = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {

    }];

    [alert addAction:actionAdd];
    [alert addAction :actionCancel];

    [self presentViewController:alert animated:YES completion:nil];
        }
        if (fileExists) {
        [self performSegueWithIdentifier: @"detailSegue" sender: self];

        }

    }