The manual is fairly explicit and it should be a repeat during the inventory for accurate identification of # parts (screws and washers) before embarking on this maneuver ...
But half an hour is enough to assemble the 6 long screws / washers and narrow 8 short screws / washers wide.
Note that if the handle is right, the seat tilts backward (not forward)
No fault on the chrome, or dressing chair, firm and comfortable seat, adjustable height and tilt débraiillable.
The dial (under the seat) compensates the weight to balance backward tilt.
(For me, 80 to 85 kg, is completely unscrewed)
The lever, operated from the top down, releases the adjusting cylinder height,
but laterally, it unlocks the chair in rotation / tilt.
The only gripe is that there is only locked position (it is on the right seated)