OPT Denial Letter and I-765 Form

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I am currently on H1B status and about to file I-485 for adjustment of status.

In I-765 Item # 11, there is question on "Have you ever applied for Employment Authorization from USCIS?"

If Yes, there are additional questions like "which office and results granted or denied?"

After finishing my Master's degree, I have applied for my OPT in 2003 and was denied. There was a receipt and denial letter sent to me which I don't have it now.

How should I proceed about completing this?