Just because it’s Bluetooth and connects to an app does not mean it will connect to Zwift. The Bluetooth used by the treadmill might not be open to Zwift or other 3rd party apps.
I have a ProForm treadmill that will connect to the iFit app, but it will not connect to Zwift because the protocol used is not open to 3rd parties.
Also does it broadcast in BLE or ANT+. If it broadcast in ANT+ what device are you running Zwift on?