Suppose I made an app using app inventor and want to publish that in google play store or app store. I get an estimated 10000000 users. Then I might need to use bigger data base for storing and arranging more data . How can I do that and what will be its estimated cost . I have used Cloud DB and Tiny DB in the app . Should a completely replace Cloud DB or Is there a way to modify cloud db to store more data by paying?
CloudDb probably not suitable for ten million users.
You will need a commercial online database such as Firebase or Redis.
Look through the Firebase documentation, they offer pricing information.
 tinydb should be OK for local storage on each user's device.
CloudDB is based on Redis.
You should use your own servers with such large numbers and not depend on another company for the database. Use MySql or something like that to use for the data.
If you have less users and want something easier to use, use for instance Baserow. It uses a PostgreSQL as a backend.