Inside the gear shift tube that broke off is a thin rod . If you did not damage it or are still able to straighten it out, you can remove the rest of the gear shift by removing the three torx screws (there may be tools in the back for this task). Dismantle the plastic parts and then take the entire pieces to a welder and have him weld the broken piece back in the exact same position.
($15-$20 job). Then you need to assemble the thin rod which is fitted from the top (must remove the knob by simply prying it off) and then put the spring and the reverse locking piece at the bottom by screwing it on to the thin rod. after it is assembled, put the plastic ball and the clip on and install the piece in the gear shifter housing. Temporarily install the screws and test for correct reverse action. If it goes towards reverse without a need to pull up on the lever, then remove the shifter, remove the clip and unscrew the lower piece (reverse lock) look here
