Say so directly in your message. Explain what the document is needed for, when you need it, and which document you believe will solve the problem. Support can usually work faster when urgency is explained clearly and specifically.
If the deadline is linked to a school, provider, or official appointment, include that timing in a calm, factual way. “Needed today for hospital admission review” is much more useful than “urgent please”.
If you already have one relevant document, attach it so support can cross-check the record quickly.