How to properly call Async Task

I have this async task, and I am calling it with a coroutine, but it stops briefly the game and I want it to run on background so it DOESN'T stop the main thread at all. This is the coroutine that calls the async task. I don't know what to do to run it smoothly. Please help and thank you!

 // Coroutine that calls the async method GetNewSong
 IEnumerator AsyncDownloadSong()
     {
         downloadBtn.interactable = false;
         deleteBtn.interactable = true;
         customManager.GetNewSong(s3File);
         yield return new WaitForSeconds(0.1f);
     }
 
 // Async task that awaits async method
 public async Task GetNewSong(string pFile)
     {
         await awsManager.GetZip(pFile);
     }
 
 // Async task that calls and AWS method. 
 // The important thing is that is async, the aws logic is fine and saves 
 // the file where is supposed to be
 public async Task GetZip(string pFile)
     {
         string folder = "Assets/Audio/Custom/";
 
         try
         {
             GetObjectRequest request = new GetObjectRequest
             {
                 BucketName = S3Bucket,
                 Key = pFile
             };
             using (GetObjectResponse response = await S3Client.GetObjectAsync(request))
             using (Stream responseStream = response.ResponseStream)
             {
                 string title = response.Metadata["x-amz-meta-title"]; // Assume you have "title" as medata added to the object.
                 string contentType = response.Headers["Content-Type"];
                 Debug.Log("Object metadata, Title: " + title);
                 Debug.Log("Content type: " + contentType);
 
                 if (responseStream != null)
                 {
                     using (BinaryReader bReader = new BinaryReader(response.ResponseStream))
                     {
                         byte[] buffer = bReader.ReadBytes((int)response.ResponseStream.Length);
                         File.WriteAllBytes(folder + S3SampleFile, buffer);
 
                         Debug.Log("Writed all bytes");
                         StartCoroutine(customSongsManager.ReadDownloadedSong(folder + S3SampleFile));
                     }
                 }
             }
         }
         catch (AmazonS3Exception e)
         {
             // If bucket or object does not exist
             Debug.Log("Error encountered ***. Message:"+ e.Message + " when reading object");
         }
         catch (Exception e)
         {
             Debug.Log("Unknown encountered on server. Message:"+ e.Message + " when reading object");
         }
     }