Read the evidence rule
Check whether your university accepts evidence after the original submission, and at which stage. Some review stages examine only whether the first decision was made properly, while others can consider genuinely new material.
Explain timing and relevance
Identify what the document shows, when you obtained it and why it could not reasonably have been provided earlier. Link it to a particular appeal ground and decision, rather than sending a large set of material without explanation.
Keep the record complete
Save requests for records, responses and submission receipts. If a document is still pending, say so before the deadline and ask how supplementary evidence should be sent.