Identify the decision, not just the screen.
Tell us what someone needs to finish. A service inquiry form has a different job from a staff screen used to approve a record. Start there. Existing page addresses or a short description of the current route can be enough for an initial conversation.
You do not need to prepare a technical specification before getting in touch. We do need to know who uses the interface and what currently prevents the intended result. Keep private records and credentials out of the inquiry.
Decision at this point: whether the request is suitable for further scope discussion and what information is needed next.