Planet Tax Refund Office at Helsinki Airport is located in the Arrivals hall next to the taxi station.
When the office is closed, you can get a stamp from Customs, which is located in the entrance hall in front of the taxi stand, 1st floor, and at the gate 29. Fill in all your information (passport number, name, address, credit card number) in the form and leave your tax free form with the Custom stamp in our return box.