Here's a link to the BMW UK web page for air-con servicing:
https://www.bmw.co.uk/bmw-ownership/...ioning-service
Particularly useful is this section from the page:
BMW Air Conditioning Refresh.
Is your BMW starting to lose that new car smell? It may be time for a refresh service. We want your drive to be as comfortable as possible and we have the expertise to make that happen; we recommend you take your BMW to your local BMW Centre so a highly trained BMW technician can clean and disinfect the evaporator and air duct systems, as well as treat the air vents and the interior to keep that new car smell for a little longer.
As indicated by
Abh29, It may be worth checking with a local BMW specialist to see what price they may charge and then talk to your dealer to try and get them to price match.