If your Hisense TV runs VIDAA 4, VIDAA 3, or VIDAA 2.5, you should have access to the Tubi app.
It will be available as one of the pre-installed apps on your TV. There is not currently a way to install it manually if you don't already see it available on the TV.
If you have a Hisense Roku TV, please see our Roku help articles here.