The MySOS app is no longer available after 14 November 2022. Instead, Visit Japan Web taken its place. - Quarantine for entering Japan | CoDigital, inc.
For Travelers | COVID-19: New Normal Travel in Japan | Travel Japan(Japan National Tourism Organization)
PART 2: TO ANYONE ENTERING/RETURNING TO JAPAN ON OR AFTER NOVEMBER 14, USE VISIT JAPAN WEB NOT MYSOS - YouTube
1_MySOS Web : Pre-registration for Quarantine procedures - Teachme Biz