The fill port is on the left side (sitting in tractor seat) of the tractor. It is on top of the steering box which is bolted on top of the clutch housing.
It will be difficult to see but bend your head down into the shifter area and look forward under the dash cowling. On my tractor it is beneath the fuel tank and the steering column comes down through the fuel tank.
The red object (pen) is pointing at the square head pipe plug that is the fill port.
In this picture the red object is touching the plug
You can see that area is very dirty so you may need to remove debris and oily residue to see it