This technique is sometimes called a “bookends” approach because it positions your introduction and conclusion as related ends of your document. The basic idea is to turn your conclusion into an extension of your introduction.
If your introduction uses a quotation, end with a related quotation or respond to the quotation.
If your introduction uses a story, extend that story or retell it with a different ending.
If your introduction asks a question, answer the question, restate the question, or ask a new question.
If your introduction defines a problem, provide a solution to the problem, restate the problem, or suggest that readers need to move on to a new problem.