Question

(narration change) he said to me "have you bought a com puter"​

Answer 1

Question -

He said to me, "Have you bought a computer ?"

Answer -

He asked me whether I had bought a computer.

Explanation -

First notice the tense of the sentence. The presence of have and bought signifies it is in present perfect tense.

Accordingly, when you change the narration, the given tense changes to past perfect tense.

i.e, have becomes had.

Since it is Y/N question, we use whether/if

He asked me if I had bought a computer - it is also correct.

Summarizing ,

present perfect tense - have+ past participle of verb

changes to

past perfect tense - had + past participle of verb.

Hope This Helps You!