seat reservation refund

Hi,

I recently travelled from Copenhagen to Hamburg and back with Interrail global pass and for both of the journeys a substitute train was used so the seat reservations couldn't be used. The conductor on the train told us to forget the seat reservations, just find a seat and get a refund afterwards. The seat reservations were bought from DSB (Cph-Hamburg) and DB (Hamburg-Cph). I don't seem to be able to find instructions on how to claim back the seat reservation costs from either of the companys. Can anyone guide me on where and how to do that please? We travelled as a family of 4, can I do that for all of us on the same form since the reservations were bought together? Appreciate any help!