Your statement letter (why you are asking)

The statement letter is your explanation to the USCIS officer: the concrete purpose of the extra time, the dates involved, how the stay is funded, and your ties and intent to return home. It must be specific — "I want to stay longer" is not enough. The assistant interviews you briefly, then drafts the letter in English (USCIS filings must be in English). You can read it, edit it, or have it rewritten, then it goes in your package to be signed with a pen.