If you're searching for more, there's search points all around their role, their pain point, their industry. Find very specific words that people with your pain point actually use to search. Not just "best app to do X" but really what are they posting about and how do they talk in public? IF not then you'll have to do some cold emailing, cold DM's, You'll have to talk to people.

Get on their laptops and install something for them or sit down at their desk and see what they are doing and how you can help.

But from what you provided, I would make sure you really get to the bottom of why this pilot happened with your customer: did they have a problem specific enough? What changed right before they came to you (a new hire, a new regulation, a system that broke)? Who felt the pain, and who signed? Write those down as attributes, and your ICP becomes "companies that match the trigger," which is often not the same as "companies in that vertical."

All I can say is that, for most startups, narrowing the ICP is good advice; but I've seen one tool where it wasn't.

What makes it difficult?

What else is more important?