Many cyclists want the ZCA to log activity on Apple Health/Fitness and the process on how to do this is well documented. Using the Apple Watch as the HR sensor is key to this process (which can itself be connected to a HR strap).
Currently the process is currently very unreliable and a lot of patience is required for the whole thing to work. Sitting at the pairing screen for 10mins for it all to catch up is common. Can this be improved especially with Apple Health now allowng power, cadence and speed data to be logged with Watch OS10.
My understanding is that the Apple Watch Companion app itself isn’t that great and isn’t currently being developed.
However, if you connect your HRM to your watch and to the Companion app on your iPhone in the Bluetooth settings, you’ll get good data to Zwift, and the app will also log this on the related activity on your phone.
In short, I’d uninstall it from your Apple Watch and use the iPhone Companion app.