Lift the seat and you can get a good visual of the shifter and links it fits in for different gears. You can then move it. It may take a little more pressure but it will shift into neutral. This happened on my 3616 also. Its not a great design but my tractor has done everything I asked of it and more.
The Mahindra guy came over and did just that. He got underneath the tractor. He grabbed the knuckle below and shifted it into neutral, He then filed the detent "teeth" down about 1/16". It shifts smoothly now.