If the contract amount exceeds the limit, the supplementary agreement shall be written and signed by both parties. According to the provisions of the Civil Code of China, if the amount of the contract exceeds the limit, it can be solved by means of a supplementary agreement, which should be written in writing and signed by both parties. The supplementary agreement is the supplementary part of the main contract. It supplements the parts that are not agreed, unclear or prone to disputes in the contract.
 Legal basis
 Article 510 of the Civil Code of the People's Republic of China
 After the contract comes into force, if the parties have not agreed or clearly agreed on the quality, price or remuneration, place of performance and other contents, they may supplement by agreement; If a supplementary agreement cannot be reached, it shall be determined in accordance with the relevant provisions of the contract or the transaction customs.

 Article 543 of the Civil Code of the People's Republic of China
 The parties may modify the contract if they reach consensus through consultation.