You do not need to arrive with screen designs or technical specifications. The most useful starting point is a description of what happens today and where the work slows down.
Describe who uses the process, what information they need, and what a successful outcome looks like. Concrete examples of recent work are more revealing than a broad feature wish list.
From there, separate the essential first workflow from the ideas that can wait. This keeps the project focused and gives everyone a clearer way to judge whether the software is helping.
A good scope is a shared understanding, not a long document for its own sake. It should be clear enough to guide decisions and flexible enough to improve as you learn.