Enable the Elemnt app to receive heart rate from the Apple Watch and then transmit the HR to the bike computer via BLE. There are apps that do this, such as HRM app but they are clunky since they take over the Bluetooth connection to the bike computer and it’s impossible to use the Elemnt app and HRM app simultaneously.
This feature would make it possible to use the Apple Watch as the HRM for Wahoo computers, and avoid using a strap HRM.