Change the narration: Nazir said, "I did my duty with full justice."

Change the narration: Nazir said, "I did my duty with full justice."

Explanation
Direct Speech: Nazir said, "I did my duty with full justice."
In indirect speech:
"I" becomes "he" (subject change)
"did" (past simple) becomes "had done" (past perfect) to maintain the timeline correctly in indirect speech.
So, the correct indirect speech would be:
Nazir said that he had done his duty with full justice.