I recommend thinking about these questions:
1) Is this worth solving?
2) Why us? Why now?
3) How Might We break up the problem? What sub-problems should we go after(repeat steps 1-2) ?
In general, the main thing I look for when validating any problem or solution is data. As a PM, it is important for you to figure out where to get the right data for what you are validating.
For example, if it's a problem statement around a user need or pain point, the first step would be to run user research panels to get data directly from users or potential users. I recommend you augment that with market research data such as independent analyst reports, research reports published by competitors of their user base, and related user data available to you such as broad user surveys.