Aside from everything the other experts covered, I would give you one easy recommendation:
1. Build out a quick landing page clearly explaining your product/service and make it interesting.
Set it up as a "coming soon" page with an email field so customers can be notified when it launches.
You can have this done by a designer or use a service like Instapage, Leadpages, Unbounce, etc that makes it easy for you to do it yourself using templates.
2. Send a bunch of people to your landing page using Adwords, Facebook Ads, etc.
Make sure you specify your market clearly so you only target the appropriate people (there are many courses out there on how to do this).
3. If you get a good response (many people signing up), you know there is a market for your product/service.
You can then capitalize on the list you created by giving everyone that signed up a discount or free trial once you launch.
Let me know if you try it out!