Ask the customer for a referral to someone who has the same pain point. Let them reach out to your future customers for you.
What you should do is just talk to users. People who are actually using what you're building.
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.
