You can negotiate and sign a supplementary agreement before the developer; If the negotiation fails, you can bring a lawsuit to the people's court.

Legal basis:

After the entry into force of Article 511 of the Civil Code of the People's Republic of China, if the parties have not agreed or clearly agreed on the quality, price or remuneration, place of performance, etc., they may supplement it by agreement; If a supplementary agreement cannot be reached, it shall be determined in accordance with the relevant provisions of the contract or trading habits.