There is no actual overview of all available regions in one file or map. But you can find the regions you are looking for either in the App under "Regions" (Globe Icon) > Search or online via a right-click on the map or entering a city name of your choice in the search field. On the Android app, you'll find the search field by tapping the magnifying glass icon on the bottom right side.
An overview of all countries currently contained in the Complete Package can be found here:
Direct Link: Complete Package
Tipp: Instead of downloading entire regions, you can save single planned Tours with the required maps on your mobile device. This is especially useful if you are planning a long Tour crossing several regions or want to save space as you only marginally cross some of the regions while passing. Open a planned Tour in the komoot app and use the toggle "offline available", then wait for the Tour to be downloaded and marked with a pin icon.