That depends on the type of motor. If it has a permanent magnet for the field it should be easy, if it has a wound field it's still not difficult but slightly more involved. It would also help to know how the reversing was performed with a.c.
The plug-in board looks very much like the Delta decoder that came with my MAXI loco, and which I replaced with a DCC decoder. My loco has a DC motor and also comes with a DC adapter board, Marklin part 66802. You just need one of these (on the left) I think?
It should be easy to make an adaptor if you can`t find the Marklin part. The diodes are only there for the directional lights, and the adaptor plate bridges the track pickups to the motor connections.
I made an adaptor board for my DCC decoder from standard copper-strip board, like this: