code: def add_to_timestamp(timestamp, time_delta,
                       str_format='%Y-%m-%d_%H:%M:%S.fff'):
      
      date_time = str_to_datetime(timestamp, str_format) + time_delta
      return datetime_to_str(timestamp, str_format)
docs: This will convert the timestamp to datetime, add the timedelta
          and then return it as a timestamp
      :param timestamp:    str of the date and time
      :param time_delta:   datetime.timedelta of the time to add
      :param str_format:   str of the format of the timestamp
      :return:             str of the new timestamp