Question

he told me the truth during our conversation
change into double objects passive voice

Answer 1

The truth was told by him during our conversation.

Hope it helps :)

Answer 2

The Truth was told by him during our conversation.

In the active sentence, the subject is before the predicate, while passive, the subject of the sentence is placed after the verb in the object position.

Turning an active sentence with two objects into the passive sentence, now there are two objects in the sentence.