SSC MTS 2 Aug 2019 Shift 2 Paper

Correct option: 2) had reassured me - this is the most suitable option.
It is clearly visible that the sentence is in the past tense, since rest of the options are in present tense so we can easily negate rest of the options.
Also, the operating process succeeds the event of the doctor reassuring me. Thus, 'had reassured'-the past perfect form is apt in the given context.
Hence, Option 2 is the correct answer.