Write down the sentence in reported speech. "I have just received a letter from my uncle," he said.

Чтобы перевести предложение из прямой речи в косвенную, нужно изменить структуру предложения, а также, возможно, изменить времена глаголов и местоимения.

В данном случае, прямая речь: "I have just received a letter from my uncle," he said.

В косвенной речи это будет выглядеть так:

He said that he had just received a letter from his uncle.

Ответ: He said that he had just received a letter from his uncle.