Hi Garry, Welcome to English Forums! 1) 'she did not have' ('has' is 3rd person PRESENT tense only) 2) 'he doesn't have' (only the auxiliary 'do' takes the 3rd person '-s'. Another way to remember is: only one 's' in the verb phrase.
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Third person singular (he, she, it, who, which,...) works as follows.
Present affirmative. Present negative. Past affirmative. Past negative.
She has a coat. She does not have a coat. She had a coat. She did not have a coat.
In the present tense, one and only one verb has the present marker s.
In the past tense, one and only o