Whether you have a regular ticket or a reservation (with a Eurail pass), you need to contact the place where you bought it.

If you bought a pass reservation through Eurail, then contact customer service here:

https://eurail.zendesk.com/hc/en-001/requests/new

Eurostar pass reservations are normally not refundable, only changeable for a fee.

Thanks for your reply, I would like to contact the customer service!

Have a nice day :-)

Btw there are no riots anymore in France and the situation has always been pretty safe as long as you didn't go to the suburbs at night.

Life goes as usual.

There's no real need to cancel your trip imho