Question

he told us his past experiences

Answer 1

Hey Dear!
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I think that you have asked to change the given sentence into passive voice. 

Given sentence- He told us his past experiences.

Passive Voice-

We are told of his past experiences.
OR
His past experiences were told to us.

Explanation:
In the given sentence, two objects are given and therefore, it can be changed into passive voice in two ways. In the first passive voice sentence an additional word, a preposition, "of" has been added to complete the sense of the sentence. Note that the "by agent " is missing here.
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Answer 2

We were told his past experience by him.