@Mahwesh, your friend sweetypurplerocks has put in a lot of efforts in trying to help you out. However, here is the correct solution to your query.
(1)A song is being sung by me.
(2) The bell is being rung by him.
(3)My work has been completed.
(4) The child was flying a kite. This sentence cannot be changed into passive voice as ‘fly’ is an intransitive verb.
(5) A novel was being read by them.
(6) A letter was written by him.
* Tell the truth. Do not tell a lie. Stop it. None of these sentences can be changed into passive voice.
@ sweetypurplerocks, your efforts to help your fellow students are commendable and encouraged at our forum. Bravo! Keep it up!