Probably the reason that this is difficult is that most pre-purchased French train tickets are not refundable (which is not the same in Germany). The computers are programmed to follow normal refund rules according to fare type, not to make exceptions in the case of a strike.
Similarly, if you have bought your French ticket from Rail Europe, this is the procedure they describe:
If your train is cancelled, or if you prefer not to travel during a strike day, the below refund conditions apply:
If you are in France, you can choose to go directly to a railway station and ask the local railway official to assist with:
• Providing an update on the status of your train
• Providing alternate transportation options that will be covered by your existing train ticket (no extra costs)
• Changing the date or time of travel using your existing train ticket
• Endorsing your ticket as ‘unused’ if it will not be used for transportation provided by the railroad
One the ticket has been endorsed by a railway official, you would next contact Rail Europe to receive instructions on how to proceed with obtaining a refund. All relevant documentation needs to be received by Rail Europe within 45 days of the scheduled departure.
If you are not in France, you can contact Rail Europe before the train departure to start the refund process. DO NOT try to refund the tickets from your online account as this will incur the regular after sales fees for these tickets. After the initial refund request has been received by Rail Europe, you have up to 45 days after the train departure to forward Rail Europe all relevant documents.
Connecting trains, not operated by SNCF, may also be eligible for refunds. Please follow the same procedures as outlined above to apply for a refund for connecting trains impacted by the strike.
In case of Paper tickets please make sure you send the original unused ticket via express traceable mail as no refund can be guaranteed should the tickets not be received by Rail Europe. If applicable, also include any replacement tickets along with a letter explaining the occurrence. Once endorsed tickets are received, Rail Europe will submit to the railroad on the customer behalf. In case of dispute, any compensation is at the sole discretion of the railroad. We regret to inform you that no refund will be possible for tickets/requests returned later than 45 days from date of travel.
Should you choose to travel on a strike day:
• If your train is confirmed to be operating, we advise you to arrive at train station early. Due to a possible increase in passengers, you may experience longer than usual time reaching the departure platform and boarding the train.
• If your train has been cancelled once at the station, you can verify from the live departure board which trains are confirmed to be operating. You will be entitled to travel on any train on the same route of your original ticket within the same day without additional fees.
Seating cannot be guaranteed and no compensation can be claimed should you not be able to find a free seat on board, nor for any discomfort experienced during travel as this national strike is beyond the railway’s control.