"Don't repair the computer yourself," she warned him.

1. She warns him not to repair the computer himself.
2. She warned him not to repair the computer himself.
3. She will warn him not to repair the computer himself.
4. She should have warned him not to repair the computer himself.

Converting direct speech with imperative to reported speech requires backshifting the reporting verb to past tense: “warned” (not “warns”). The correct form is “She warned him not to repair the computer himself.” The reflexive pronoun “himself” correctly refers to the subject “him.” This transformation maintains the warning while adjusting tense and pronoun reference appropriately for reported speech conventions.