I was wondering how to get power, speed and cadence from Wattbike to Garmin connect without Wattbike hub app and Wattbike instructions were a bit vague. Basically I first verified that ANT channel was configured correctly as instructed in Wattbike instructions. I didn't have to change anything. Then while Wattbike was on I opened sensors & accessories on my Garmin watch and added "Spd/Cad - 12345" and "Pwr - 12345" sensors and started the session. The five number ID: 12345 is located on the bottom of the main screen. There are a lot of sensors available at the gym so I would check the ID carefully before pairing.
I hope this helps!