My Grohedal cistern actuator has broken?

My son was pounding on the wall button and broke the piece that the button pushes on to flush the toilet (it is like a red plastic rod). It is a single flush type and not pneumatic in any fashion (seems like all of the flush valves I see on internet searches are pneumatic now). Pushing the broken part in (towards back of toilet) horizontally lifts a whitish vertical tube, flushing the toilet. I am hoping to not to have to buy a whole new valve since I just rent this apartment. All of my searches for actuator just give me the exterior push buttons. Any help identifying the necessary piece, part number and where to buy it would be greatly appreciated.