Official steps: unfold the scooter; insert handlebar stem into the fork tube without pinching cables, connect the stem-to-handlebar cable; insert and tighten the 6 supplied screws with the supplied hex key; verify the handlebar does not move relative to the stem, re-tighten if needed; check tire pressure is within 2-2.4 bar before first use.
Fuente oficial: https://www.wispeed.net/?controller=attachment&id_attachment=6 (tier A). Traducción/paráfrasis fiel del manual oficial; no se ha añadido ningún procedimiento no documentado.