How do install it on Hitachi? I can find it in the apps list.
If it’s not on this list of supported devices then you can’t install it.
https://help.nowtv.com/article/what-devices-can-i-use-to-watch-now
I suggest you get yourself an Amazon Firestick, which Amazon are knocking out at good Black Friday discounts right now.
This will provide your Hitachi not just with Now, but with a whole panoply of other smart apps to choose from.