Apple Watch bought in Apple Store Brooklyn not working in Feance

You made an unfortunate buying decision. All Apple Watches made for the US market, support cellular bands in the US, Canada, Mexico and Puerto Rico. You cannot exchange the watch even with the 14 day return window in France. You could hop on a plane and come back to the US, if you're still within the return window and return the watch for refund. But that would be pretty expensive. Your most realistic options are:

1. Sell the watch to someone you know in one of the markets the watch was designed for
2. Use the watch as a GPS only watch, meaning it will work just fine as long as you have your paired iPhone with you

you can try to sell it, the cellular models from usa, canada and mexico does not work anywhere else