you can refer to this sample:

https://github.com/awslabs/aws-sdk-ios-samples/tree/master/S3TransferUtility-Sample/Swift

Snippets and important parts from the above sample:

SDK initialization:

Copy this into your info.plist:

https://github.com/awslabs/aws-sdk-ios-samples/blob/master/S3TransferUtility-Sample/Swift/S3BackgroundTransferSampleSwift/Info.plist#L73

Upload Code :

let transferUtility = AWSS3TransferUtility.default()
let expression = AWSS3TransferUtilityUploadExpression()
expression.progressBlock = progressBlock

transferUtility.uploadData(
            data,
            bucket: S3BucketName,
            key: S3UploadKeyName,
            contentType: "image/png",
            expression: expression,
            completionHandler: completionHandler).continueWith { (task) -> AnyObject! in
            if let error = task.error {
                print("Error: \(error.localizedDescription)")
                self.statusLabel.text = "Failed"
            }

            if let _ = task.result {
                self.statusLabel.text = "Generating Upload File"
                print("Upload Starting!")
                // Do something with uploadTask.
            }

            return nil;
    }