Do it. Please change this sentence into passive voice.

This is a good question!  In order to have the passive voice, words need to be arranged so that what would ordinarily be the subject in the sentence, the word that performs the action, is relegated to a lesser role, usually an object of a preposition.  In the sentence you have provided, the word "you" is implied, and this is the subject of the sentence.  If we fill in the implied word, we have:

        You do it.

Thus, "you" is the subject, "do" is the verb, and "it" is the object. 

Now, how do we make this passive?  We make "It" the subject and we put "you" in a prepositional phrase.  Because we cannot say "it do," and because even "it does" does not convey the correct meaning, we do have to make a change.  How about "It needs doing" or "It needs to be done."  Both of these convey the same meaning and preserve the verb.  In order to place "you," the original subject, in a prepositional phrase, we can say, "It needs doing by you," or "It needs to be done by you."  Now, the original subject has become the object of a prepositional phrase and "it" is the subject. 

Do you see how ineffective it can be to write in the passive voice?  We do need it sometimes and no writing can avoid it completely, but a statement is usually stronger when written in the active voice.  The passive voice is often referred to as "the weaselly passive voice" because if there is no person in the sentence doing something, it seems like that person is avoiding responsibility. Contrast these two statements:

           Mistakes were made by me.

           I made a mistake.

Which do you feel is the more honest and forthright statement?