Lenovo ThinkVision and Apple TV via Chromecast

Apologies if this has been asked already. It's a pretty specific question. I just set up a Lenovo ThinkVision monitor and then connected a Google Chromecast with Apple TV. During the setup there is a check of the volume and the power buttons. It asks for the type of TV or other device I am trying to set up. At no point in any of the list of manufacturers does IBM, or Lenovo or ThinkVision come up. What should I use to set this up? As it stands now everything works but the volume. Thanks in advance.