Which immigration office do I visit to extend my TR60 visa in Thailand, and is it true I should go 3 days before expiry?

The user is seeking information on where to extend their TR60 visa in Thailand, specifically if they can obtain an extra 30 days or a Covid-related extension. They mention their visa is due on the 10th and question whether they should visit the immigration office 3 days before the expiry date. One commenter advises that the main immigration office at the Government Complex on Chaengwattana Road (Counter J) is the correct location to go for an extension, and they confirm the recommendation to visit when there are 3 days or less remaining on the current visa stamp.