Pass the end of a pencil or biro through the flapped aperture at the bottom left of the gear selector panel and push down. This will release the selector.
I'm guessing your brake lights will not be working which means you will need to replace the switch by the brake pedal. About £9 from the stealership
Most likely to be the selector module, sit in the car with the ign on, put hand on gear lever and press brake pedal, you should feel a light tap from it, if so all is correct and the plastic lever has broken inside shift mech. New gear shift req