In this study, we analyzed the reaction of the upper atmosphere to an increase in illumination after the solar flare on 6 September 2017. This intense solar-terrestrial disturbance event was caused by the active region of the Sun AR2673, which generated several powerful X-class flares. The strongest X9.3 flare occurred on 6 September 2017 inducing an increase in illumination in the extreme ultraviolet and soft X-ray ranges of the solar spectrum. We used the FISM2 empirical model to derive the flare irradiance data and the HAMMONIA 3D high-top chemistry-climate model to study the related atmospheric effects. We showed that the event has significantly affected the upper atmospheric chemistry and produced up to 300% increase in odd nitrogen around 80 km.