Start with any existing diploma, transcript or institutional correspondence and request official replacements from the appropriate records office. Identify the precise missing fact, such as award of the degree or the courses completed. Keep names and dates consistent and explain genuine changes with supporting records where relevant.
Use a retrieval plan that follows the gap
Ask the custodian about archived records, replacement procedures and available verification formats. If the school has closed, investigate the designated successor or archive without assuming one exists. Save responses showing what was requested and what can be supplied.
The fact that you made repeated requests does not itself establish the qualification. If records remain unavailable, have the evidence problem assessed before filing; acceptable alternatives depend on the applicable procedure and facts, and should not be invented for convenience. Order the retrieval by how long each item is likely to take rather than by how important it seems.
Requests to institutions abroad, to archives and to bodies holding records for closed schools sit at one end and should go out first; documents already in a drawer sit at the other. For each request, record the body approached, the date, the reference given, the response and any fee paid. Ask each institution what it can actually produce, since a registrar may be able to issue a statement of attendance and completion where a full transcript no longer exists, and knowing that early changes what you ask for.
Keep professional registration records, continuing-education certificates and employer letters in a separate group, clearly labelled, since they speak to practice in a field rather than to the academic requirement and should not be presented as though they answer it.