2023 Trophy FL here (registered July 2023).
Some dealers seem completely unaware of the issue. My two closest (Brindley Cannock and Wolverhampton) knew straight away what I needed, with Cannock quoting £159 and Wolverhampton £96.
I did try the dealer in Rochdale as I work in that area every week, but they didn't seem to know anything about it and suggested £140 minimum, plus extra depending on what was needed.
For the amount of times I charge out and about it's not worth me forking out to get the update done.
Understandably dealerships won't do work free of charge as they have costs to cover, so it's frustrating MG don't cover this under warranty, or at the very least, cover it free of charge along with a service.
Update: Budgen MG Telford confirmed that MG cover this so I've booked in there for the update FOC.
Update 2: Budgen emailed me to apologise and confirm the update is chargeable. They advised MG originally covered this, but policy has now changed and it is chargeable for FL cars.