The fish was cooked by Sudha.
Passive voice is basically the reverse version of Active voice. Here are how the sentences go:
Active Voice: Subject + Verb + Object.
Passive Voice: Object + Verb + Subject.
For example, “Gina and Reza are going to play soccer” is an Active Voice sentence because it goes like Subject + Verb + Object. “The soccer ball is going to be played by Gina and Reza” as a Passive Voice sentence because it goes like Object + Verb + Subject. I hope this helps!