Air Con Cleaner, its made by Comma, all you do is slide the passenger seat the full way forward and position it on the floor near the in the rear passanger foot well.
Then start the car and put the aircon on full tilt and make sure that the re-circulation setting has been turned on. Then set the can of cleaner off and leave the car running for 10 minutes with all doors/windows closed. I will be doing my Cupra tonight as it needs doing also after 3 years and 34k lol.