Further update, I took the bearing out, it just popped off the race, replaced with a bearing the same spec and all went straight back in again.
Dead easy
I found it useful if you have power for all your rides as it works very cleverly, but as I only put less than 1/2 of my rides on it wasn’t realy worth the extra.
I found the software that came free with the power tap to be more than adequate.
Just to update this thread in case anyone googles looking for an answer. I contacted Balfa and they confirmed the bearings are not replaceable, a new headset is required.