Hi, SNCF sells Tickets for TGV including reservations. Maybe you can cancel the reservation and only book a new ticket with SNCF. 

Thank you for your quick answer. Where can we cancel: on interail or at the SNCF?

Is it possible to get a refund for a reservation through Interrail? How?

Sometimes-but not often-and I think (not sure) that for SNCF-TGV it is only exCHANGEable-not refundable. Without proper details-which any newbee posting here does not seem to understand, how do you even think we can give proper advice? Otherwise-obviously evidently: walk/cycle eco-friendly to some SNCF counter, hope they do not strike again and ask.

Thank you for your answer. I was finally able to claim the refund on my Interail account. They will reimburse in part (60%).

And so, I will take a ticket directly to the SNCF. The remaining day of my pass will be used during our trip to Poland.

Thank you.

Thanks also for your humor:)