Official steps: if the disc brake is too tight or too loose, use a hex wrench to loosen nut (A), then adjust the brake cable (shorten it upward if too tight; pull it downward if too loose), then re-tighten nut (A). Check alignment between the brake caliper and the disc, using screws B and C to adjust position/alignment if necessary. Manual advises contacting a service centre if unfamiliar with the procedure.
Fuente oficial: https://www.platum.com/_files/ugd/03e1ee_8da4b68bd0f34fe399c6be5e41b096de.pdf (tier A). Traducción/paráfrasis fiel del manual oficial; no se ha añadido ningún procedimiento no documentado.