If there is no box at the time of application, you can fill in the declaration of advance publication of the invention patent request.
The above form can be found on the website of China National Intellectual Property Administration ("Home > Form Download").
In addition, if the PCT application is for the national phase in China, you can also fill in the 20th column of the international application statement (invention) for entering the national phase in China, and request to publish it in advance.