One way is to talk to people who (you think) are your potential customers. Most people don't do that but even those who do it, can do it badly. I recommend "The Mom Test" (my summary:
https://blog.kowalczyk.info/dailynotes/note/b4u674cvj43jdajd...) to learn how to talk to people to validate an idea.
Also, https://30x500.com/academy/ is an on-line course dedicated to that topic.
But the question shows a backwards process. You want the process to be:
1) come up with an idea
2) validate the idea
What 30x500 preaches is more like:
1) notice a problem people are having that you can solve with software
2) that is your idea
Following that process, the job changes from "come up with many idea" to "look out for signals that point to problems that are solvable with software".