Which punctuation change will correct this sentence? on my job application i listed three references: mr. stewart; scoutmaster, mrs. thomas; journalism teacher, and mr. colley; youth minister?

Using the Oxford Comma (a comma after the second item) is correct punctuation. It is correct to say, "I listed Mr. Steward, Mrs. Thomas, and Mr. Colley." It is incorrect to say, "I listed Mr. Steward, Mrs. Thomas and Mr. Colley."