def get_specific_comments(client, parent_id):
    """ Call the API's comments.list method to list the existing comment replies
    Args:
        client (IntalledAppFlow): a dedicated client registered with credentials
        parent_id (int): comment thread parent id 
    Returns:
        comments["items"]: a simple list containing comments for parent_id
    """
    comments = client.comments().list(
        part="snippet",
        parentId=parent_id,
        textFormat="plainText"
    ).execute()
    
    for item in comments["items"]:
        print("Comment by {}: {}".format(item["snippet"]["authorDisplayName"], item["snippet"]["textDisplay"]))
    
    return comments["items"]