From the owner's manual...see highlight in green. Just to add some complexity.
Every 72 000 km (45,000 mi). Change the transmission fluid andexternal canister filter. Change the external canister filter every 36 000 km(22,500 mi) thereafter. This service can be complex. See your dealer.
Or when the CHANGE TRANSMISSIONFLUID SOON message displays, change the fluid and external canister filter within the next 1 000 km (620 mi). Failure to change the transmission fluid at required intervals can lead to reduced transmission performance. The transmission fluid must be changed at least every three years and the Fluid Life System must be reset. Your dealer has trained service technicians who will change the fluid and reset the system. If the system is ever reset accidentally, the fluid must be changed at72 000 km (45,000 mi) since the last fluid change. See Dual Clutch Transmission Fluid Life System 0 252