When you have an idea, you need to start getting it out there and validated.
Create an offer around it and set up a simple sign-up page on your website (or make a one-page website to accomplish this if you don’t already have one).
Then start going out into Facebook groups, Twitter chats, Reddit forums, etc. and search for people who are facing the problem you solve.
Talk to them and answer their questions, give them real practical value up front to gain their attention and earn some credibility.
After you have a dialogue going, ask them to check out your new idea offer and if it’s something they’d be willing to sign up and pay for (until they pay, it’s not fully validated).
If you have some capital, then you can start running Facebook ads to get traffic faster and see if it’s something of interest to the people you’re targeting.
But it all starts with getting your offer in front of the right people.
Until you start putting it out there and getting feedback from the target audience, it won’t get anywhere.