Will you leave from Geneva airport? If yes, they have France side custom.
If not, I also have no idea... I travelled from Paris Gare de Lyon to Geneva by train 3 years before, I didn’t notice anywhere is Lyon station which allow you to do tax refund
Just arrived Paris, the ApartHotel that I stay is nice and worth for money. The location is prefect and the hotel is in good condition. But the 25m sq studio room is smaller that i expected which may not suit for 3 people or more. They have other bigger room
Citadines Les Halles Paris
4 Rue des Innocents, 75001 Paris, France
+33 1 40 39 26 50
https://goo.gl/maps/2cgtDkWTyYm