Because I don't know what you want to modify, so look at the basics yourself!
People's Republic of China (PRC) patent law:
Article 33 An applicant may modify the patent application documents, but the modification of the application documents for patents for inventions and utility models shall not exceed the scope recorded in the original specifications and claims, and the modification of the application documents for patents for designs shall not exceed the scope shown in the original pictures or photographs.
Detailed Rules for the Implementation of People's Republic of China (PRC) Patent Law
Article 51 An applicant for a patent for invention may, within three months from the date of receiving the notice from the patent administration department of the State Council that the application for a patent for invention has entered the substantive examination stage, take the initiative to propose amendments to the application for a patent for invention.
An applicant for a patent for utility model or design may, within 2 months from the date of application, put forward amendments to the application for a patent for utility model or design.
Where the applicant modifies the patent application documents after receiving the notice of examination opinions issued by the patent administrative department of the State Council, it shall make the modification according to the requirements of the notice.
The patent administration department in the State Council can correct the obvious errors of words and symbols in the patent application documents by itself. Where the administrative department for patent in the State Council modifies it by itself, it shall notify the applicant.
Article 52. In the modified part of the specification or the claims of an application for a patent for invention or utility model, a replacement page shall be submitted in the prescribed format, except for individual text modification or addition or deletion. Where a picture or photograph of an application for a patent for design is modified, a replacement page shall be submitted in accordance with the provisions.
Article 53 According to Article 38 of the Patent Law, the circumstances in which an application for a patent for invention should be rejected after substantive examination refer to:
(a) the application does not conform to the provisions of the first paragraph of Article 2 of these Rules;
(2) The application falls within the provisions of Articles 5 and 25 of the Patent Law, or does not conform to the provisions of Article 22 of the Patent Law, Paragraph 1 of Article 13, Paragraph 1 of Article 20 and Paragraph 2 of Article 21 of these Rules, or the patent right cannot be obtained according to the provisions of Article 9 of the Patent Law;
(3) The application does not conform to the provisions of Paragraph 3 or Paragraph 4 of Article 26 or Paragraph 1 of Article 31 of the Patent Law;
(4) The amendment of the application does not conform to the provisions of Article 33 of the Patent Law, or the divisional application does not conform to the provisions of Paragraph 1 of Article 43 of these Rules.
Article 62 If, after reexamination, the Patent Reexamination Board considers that the reexamination request does not conform to the relevant provisions of the Patent Law and these Rules, it shall notify the petitioner of reexamination and require him to state his opinions within a specified time limit. If no reply is made at the expiration of the time limit, the request for reexamination shall be deemed to have been withdrawn; If the Patent Reexamination Board considers that it still does not conform to the relevant provisions of the Patent Law and these Rules after stating its opinions or making amendments, it shall make a reexamination decision and maintain the original rejection decision.
If, after reexamination, the Patent Reexamination Board considers that the original rejection decision does not conform to the relevant provisions of the Patent Law and these Rules, or the revised patent application document eliminates the defects pointed out in the original rejection decision, it shall revoke the original rejection decision and the original examination department shall continue the examination procedure.
Article 68 In the process of examining the request for invalidation, the patentee of a patent for invention or utility model may amend his claim, but shall not extend the scope of protection of the original patent.
The patentee of a patent for invention or utility model shall not modify the patent specification and drawings, and the patentee of a patent for design shall not modify the pictures, photographs and brief descriptions.