What Suprman said. if the hand pump isn’t firm/solid, there is a fill plug for it’s reservoir to the left of the handle mechanism.
If the pump handle gets solid with the control in the “lower“ position but no cab movement, there is a restricted orifice inside the raise/lower control valve that may be clogged. The orifice controls the speed at which the cab moves up or down. There are safeties in the cylinder that cause them to lock if the hydraulic fluid flows too fast In or out of the cylinder, like if you blew a hydraulic hose. Occasionally if there are contaminants in the fluid, the safeties get clogged and they lock up and prevent the cylinder from moving. You can sometimes free/reset the safeties if you alternately pump in the raise then lower position several times.
you can determine which it is by loosening(don’t remove it, just crack it loose) the hydraulic fitting that feeds into the bottom of the cylinder and trying to pump the cab back down. If the cab cylinder starts to move and fluid comes out of that loosened fitting, the problem lies in the control valve, probably that restricted orifice.
a gentelman on youtube Helicools Helipad just made a video on how to disassemble and clean it...