They should know what flash to install, but just in case, you'll want the ECM updated to 038 997 016T.
I have seen the dealers get confused because the service action also applies to the BEW but the BEW ECM updates to suffix "R", they get confused and tell you your ECM is already updated, trust me, it is not... I think exactly this happened to imo000.
If your car has the "R" software version, which I think it does, you can install the new glow plugs yourself ahead of time and just take the car in for the flash at your convenience. It will still start fine.
If you have the steel glow plug "N" version, installing the new ceramic glow plugs will make it difficult if not impossible to start in the cold, so you may want to hold off and let the dealer install the new glow plugs just prior to doing the flash.