Remotes from different manufacturers of "Roku TVs" generally won't work on each other's TVs Some manufacturers share the same codes, but you wouldn't expect a Samsung remote to work on a Sony TV, so you shouldn't expect a Hisense remote to work on an onn TV, Roku TV or not. You need to get a replacement from Hisense or you can get a Roku Voice Remote, but for that you'll need a working remote to get it paired to your TV or you may be able to get it to pair by factory resetting the TV. You can also find universal remotes that work with Roku TVs.
As for a phone app, as long as your TV is already connected to your network (and your phone is connected to the same network/Wi-Fi) the Roku mobile app should work with your TV.
Roku Mobile App - Free for iOS® or Android™ | Roku
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