How to cancel a non- used day of a multi day pass

Hi,

I bought a 4 day pass for Interail Europe.

Today I attqched to the day the trip feom Frqnce to Germany. So it consumed one day from the pass and one in/out bound journey.

After attaching the trip, I started booming the seqt, as Thalys has seat reservation mandatory.

But as all the thalys trips had not available seats, I cancelled the booking.

But the in/outbound cannot be cancelled aa it is on the current day. Furthermore the day itself cannot be cancelled, as is the current one.

Please advise hiw can I get a refund for the unused day? I know that it was my fault, but just asking if there is any way for the refund.

Thank you

Mikel