Explanation:

Here the correct answer is Option 1.
In the above given sentence, 'him' will be replaced by 'he'.
It is so because after 'if' pronoun is used in nominative case.
• Nominative case(Subjective case) - If noun or pronoun is used as a subject, it is said to be the nominative case.
• For Ex - He is playing cricket.
• Uses of 'if' - We often use if to introduce possible or impossible situations or conditions and their results.
The situations or conditions can be real, imagined or uncertain.
• For Example - I usually make a sandwich to take to work if I have enough time.
• Therefore, the correct sentence is 'If I were he, I would not have left the job to try a career in acting'.