Building new features for an existing website and app

We who run Indians in Germany are focused on helping Indians across the globe who want to get information about life in Germany. be it Students, Professionals, etc who are looking for any sort of information about Germany. Our app and website should provide them with all the relevant info. For now, we have an app and a website with limited features. The goal is to build a lot of new features in the app and have a fully functioning website. Currently, the app has a lot of features but has bugs and is slow and we want to improve the UI/UX, performance and instill a lot of new features in the app.
Regarding the website: For now, it is a static website with just basic information about the app and us on the homepage. But the goal with this project is to have all the same features of the app also on the website. All the new features developed for the app in this phase should also be on the website.