You can apply at the immigration office 45 days before your visa expires

The Chinese Consulate in Thailand also issued this announcement. I have confirmed the relevant regulations with the Chinese Consulate because I will return to China next month. When I need to re-enter Thailand, the relevant regulations are: the date of signing the medical certificate must be Within 2 days before your flight to prove that you have not been infected with the virus in the previous 14 days, and you need an insurance contract with a sum of USD 100,000 that can be used in Thailand, otherwise you will not get a boarding pass! This rule applies to countries where China (including Hong Kong and Macao), Iran, Italy, and South Korea with more than 1,000 confirmed cases are listed as dangerous infectious disease areas outside the new crown pneumonia.