It's cable operated with adjusters on either end so you should be able to get to it. If it were mine, I would go to the transmission side, remove the cable and work it manually to ensure there is nothing wrong with the transmission or shifting fork. Then if OK, I would reset the alignment starting in the center or neutral and line up the shifter detents with the transmission's.
I should also say that these things don't just happen without reason...ie the cable adjustment just doesn't change without reason. I think something has happened...like someone shifted it while still moving. I would get ready to take it in.