We've outlined the process for getting the PM 5 to pair with Zwift. Please make sure you're following these steps for getting your bike working. If you're still having problems, submit a support ticket so we can investigate further.
We're currently investigating an issue where Zwift is unable to read power from the Concept2 BikeErg PM5 over native Bluetooth or through the Mobile Link app.
While we haven't found a workaround yet, we'll be working on getting this working again soon.