Question

change into indirect speech. he said, "Farewell, my friends."

Answer 1

He said his friends farewell
Hope it will help

Answer 2

The indirect speech does not require the sentence to be explicitly quoted as in the case of the direct speech.

The speaker must be of a third person in case of indirect speech.

The indirect speech does not use the present tense and it uses the past and present forms of tense and it is entirely different from the direct form.  

"He said farewell to his friends" is the indirect speech of the given sentence.