HOMCOM 312-065 Instructions D'installation page 14

2. Install Left and Right Sideboard.
Align the holes on B1 and B3,Use tools C3 and C4 to tighten the
screws with C9 and C10. Please do not tighten the screws until
all the screws are lock it after all is installed. The following steps
are the same.
3. Install the backrest tube and seat board.
As shown in the figure: Fix B4 and B5 in the order shown in
the figure, with the tools C1 and C4, and lock them with C5
and C6.