Depends on what you want to do....

For remote control of what the TV/player is showing, launching apps, etc see https://play.google.com/store/apps/details?id=com.videostorm.splashtiles&hl=en&pcampaignid=pcampaignidMKT-Other-global-all-co-prtnr-py-PartBadge-Mar2515-1

For using a control system remote (or Alexa) to control your TV/player, see https://play.google.com/store/apps/details?id=com.videostorm.irusb&hl=en

(later IRUSB app requires the IRUSB hardware, ~$50)

If you have a mouse to use I think you can side load the full Google Home app if you need a full GUI to control everything but as far as I know Google Assistant on ATV can already do all this with no app install needed