I think I've successfully completed the procedure.
For anybody else that may need to complete this after disconnecting the 12V battery:
The power output dial didn't move when I had the car in 'drive' with a foot on brake and the accelerator to the floor.
The display below the speedometer showed power going from the engine to the wheels, but the hybrid battery did fully charge.
When I put the car in 'park' and tapped the accelerator, the engine ran at various speeds for around 2-3 minutes before shutting off.
After starting the car again, it pulled away quite powerfully using the hybrid battery, which is something it's not done for a long time. Even in stop start traffic on level ground, it has been using the engine. I have disconnected the battery on numerous occasions and wasn't aware of the need for this procedure. Perhaps this is just a coincidence, but time will tell.
Hopefully, it has been successful and I'll see the car pulling away using the hybrid a lot more from now on.