Well, if you want to write the code yourself it would be best to learn a programming language like Java(Android) or Swift(iOS). There are tons of tutorials online, online courses, apps that teach coding, coding bootcamps, college classes, etc. You can also try posting your idea on Kickstarter to raise capital, then hire a programmer to write the code for you, but this requires others to truly believe in your idea. I’ve seen many successful software developers on YouTube who are self taught, it just takes dedication.
I think it's better to consult with pro developers first to avoid mistakes. When I decided to built my first app I found pro software developers and they helped me with that task. They also helped me to test my app before launching, it is an important stage. Now I want to become a tester too. I found useful guide about how to become a tester here https://fortegrp.com/become-software-qa-analyst-guide/ and I hope one day I'll become a pro QA analyst.