stuck in reverse range

[Boomer Mark]

I have a 1985 MF 484 with a range trans. It is stuck in reverse and I can't get it out. I googled and what I read is to take the filler plug out and use a screw driver to unlock it but the only filler plug I see is at the back of the tractor and this is the gear for the hydraulic life.

Is there a different filler plug for the range type transmission that will give me access to the gear / shaft to move to unlock it?
Boomer Mark