[Jurassic-1]

It probably sat for a while. You could spray some penetrant over the gears and slides and try to gently work the shifter. You could even add some trans fluid down the shifter hole before you put it back in. Note, Make sure the two dowels are still in the top of the trans where you twist the shifter cap down. I dropped one into a trans once. I got lucky and got it out through the drain hole. If you take it out in a field and run it slowly sometimes the motion of the gears moving will free up the shifter. If you get it to shift drain the fluid and put in some fresh fluid and start driving it more