It looks like Fire TV is built into the TV on that model.
Have you got ARC to work with other content from the TV - eg. TV channels ? If not, then make sure that you use the correct HDMI socket on both your TV and soundbar (only one will be ARC-enabled - usually labelled) and you'll definitely need to go into the TV's settings and turn ARC on - if everything is connected OK, you should have an option to change from the TV's speakers to 'Home Cinema' (or something similar) and enabling HDMI-CEC (or whatever JVC call it) will allow control of the soundbar's volume using the TV remote.
If you have got ARC to work with the TV channels but not with the apps, then that sounds like a fault. I would try a factory reset of the TV, make sure you're on the latest firmware and that everything is set up correctly.