The procedure in the manual is:
Depress the clutch pedal, and put the release handle of output driving shaft in “disengage” position. Put draft control handle and position control handle in the lowering position, remove the restored oil in the cylinder, (this is the part I don't understand) then, screw in the shut off valve at the left side of the lifter, put draft control handle in the lifting position and lock it, then screw out the oil plug of the oil outlet at the left side of lifter, mounted the outlet pipe assembly and connected it with implements. then step down on the clutch pedal and put the release handle in “engage” position, thus the hydraulic pipe line can be controlled by position control handle.