Updated: May 12, 2023
To repair a Sigma product in Japan, you can either take it to Sigma’s service station in Asao-ku, Kawasaki, Kanagawa or send in the product.
If you want to take it to the service station in Kawasaki, you must make a reservation by the day before you plan to go. To make reservations, send email to info@sigma-photo.co.jp or call toll-free within Japan 0120-9977-88 (or 044-989-7436 on a cell phone).
The service center is open M-Sat., 10 am to 5 pm.
More info: https://www.sigma-global.com/jp/news/2023/03/15/20240/
To send in your product, info in Japanese here: https://www.sigma-global.com/jp/support/purpose/repair/
You will need to send it to Sigma’s factory in Fukushima Prefecture.
Good luck.