Look under the operator platform on the left side in front of the fuel tank. There is a bottle there that is the power steering hydraulic fluid reservoir. If you lift the rubber pad up there is a hole cut in the operator deck to aid in adding fluid.
A common problem on these tractors is the factory reservoir bottle cracking and leaking. There are 3 options to fix this 1) replace the plastic bottle with a bottle made of the same material 2) replace the with a metal bottle 3) plumb the steering hydraulics into the main tractor reservoir.