Active sentences in the simple past tense have the following structure:
Subject + past tense form of the verb + object
Passive sentences in the simple past tense have the following structure:
Object of the active sentence + was/were + past participle form of the verb + by + subject of the active sentence

Changing an assertive sentence into the passive

Active: He wrote a letter.
Passive: A letter was written by him.
Active: They knew it.
Passive: It was known to them.
Active: She sang a song.
Passive: A song was sung by her.
Active: He loved his friends very much.
Passive: His friends were loved very much by him.

Changing a negative sentence into the passive

Active: She did not know anything about it.
Passive: Nothing about it was known to her.
Active: Nobody could discourage him from pursuing his path.
Passive: He could not be discouraged from pursuing his path by anybody.
Active: You did not listen to me.
Passive: I was not listened to by you.
Active: She did not write a story.
Passive: A story was not written by her.

Changing an interrogative sentence into the passive

Passive forms of these sentences begin with did. If the active sentence begins with a question word, the passive sentence will also begin with a question word. If the active sentence begins with who or whose, the passive sentence will begin with by whom or by whose. If the active sentence begins with whom, the passive sentence will begin with who.

Active: Did he break the window?
Passive: Was the window broken by him?
Active: Where could you find such fine art?
Passive: Where could such fine art be found?
Active: Why did you abuse your servant?
Passive: Why was your servant abused by you?
Active: Did anyone steal your purse?
Passive: Was your purse stolen by anyone?
Active: Did anyone hurt your feelings?
Passive: Were your feelings hurt by anyone?
Active: Did Alice invite you?
Passive: Were you invited by Alice?
Active: Who killed the snake?
Passive: By whom was the snake killed?
Active: Why did he punish you?
Passive: Why were you punished by him?
Active: Whom did you laugh at?
Passive: Who was laughed at by you?