You can just resign in writing 3 days in advance, and if it is not approved then, you can complain to the Human Resources and Social Security Bureau.

according to the law of the People's Republic of China and the Labor Contract Law of the People's Republic of China

Article 37 An employee may terminate the labor contract by giving a written notice to the employer 3 days in advance. The employee may terminate the labor contract by notifying the employer three days in advance during the probation period.

article 89 if an employer violates the provisions of this law and fails to issue a written certificate of dissolution or termination of the labor contract to the employee, the labor administrative department shall order it to make corrections; If it causes damage to workers, it shall be liable for compensation.

article 89 if an employer violates the provisions of this law and fails to issue a written certificate of dissolution or termination of the labor contract to the employee, the labor administrative department shall order it to make corrections; If it causes damage to workers, it shall be liable for compensation.