This is the past simple tense. In questions and negatives we use 'did' / didn't + infinitive (come/enjoy/see/go etc.): Did he come? He didn't come. He came.

السلام عليکم

didn't+infinitive

Sir didn't come is correct. If he DID come, you would say "Sir came". Although usually you wouldn't call someone sir in that context. It would be better to say "Mr. Smith (whatever his name is) didn't come"