Although I am not an expert in this field. But I can recommend an article
https://thehotskills.com/steps-to-building-your-own-mobile-app/. The author presents the material very well, so I think it will help you. Well, in general, such cases should be trusted only professionals. They know all the nuances. By the way, the author of that article is a very good expert in this. I think he even does projects to order. You read it, and then decide whether you need it or not.