1. If you have a mobile device with the Chrome app, the video player itself on your device should have an icon to recognize the Chromecast nearby.
2. If you can also try using a laptop or desktop browser, please enable Chromecast to stream your entire screen. It does not appear that the video player itself has a function to enable Chromecast specifically, but you can stream your screen to the TV and put the video on full-screen mode.