The answer to this varies depending on your operating system. Usually, the settings for split screen mode is found in your control panel under display settings.
You will need to make sure your TV is connected to your computer by an HDMI cable, or wirelessly via a mini-computer like the Intel Compute Stick.
If you are using a Mac, please follow THESE instructions.
If you are using a PC, please follow THESE instructions.
Once you have the split screen mode set up, go to your whiteboard in Chrome (in incognito mode). Expand the whiteboard as shown below and drag it over to the TV.
Finally, use the key combination for your operating system to 'full screen' your window: