Once you change it, the next reading uses the new details.
We'll read the three pillars (year, month, day) without a birth time.
South Korea · Seoul — Time zone Asia/Seoul · Latitude 37.57° Longitude 126.98° The time zone is used for BaZi and Zi Wei Dou Shu; latitude and longitude are used for Western and Vedic astrology.
If you were born outside South Korea, please change this. The solar terms occur at the same instant worldwide, so using the wrong local time can shift your entire BaZi chart.