The Echelon Fit app does not support connection to Apple Watch directly but this can be achieved via a 3rd party app, ie Blueheart or HeartCast which would need to be installed on both your Apple Watch and iPhone / iPad.
Info from BlueHeart app description:
"We follow the Bluetooth SIG spec for a heart rate monitor to turn your watch and phone into a universal Bluetooth heart rate monitor.
Using Apple Health to record your workouts you can close your rings and have your heart rate data show up in your exercise equipment dashboard"
Info re Apple Health:
The Health app consolidates data from your iPhone, Apple Watch and third-party apps you already use.