My seat hinge will not release...what do i do?

Hi, i purchased my car second hand on saturday 3 door hatch holden barina, and both seat hinges worked fine. saturday night a passenger tried to get in to the back seat and the hinge on the seat of the passenger side came off and now even without that on will not release - its like something is jammed now? do i have to take the seat apart or is it a quick job for someone at a garage to fix?

thanks for your help