Multiple backup save data

i create a fitness app, but i need to backup savedata as personal activity and exercises, but if i use tiny web db all the smartphone use the same data.
I want that if an user uninstall and reinnstall my app in another device app inventor can automatically read the google account mail, for example and tiny web db can retrive his savedata, because i create a list for example called pippo@gmail.com_exercise1 for one users and jack@gmail.com_exercise1 for another users in another smartphone, but must be automatic, because i don't want that users must write their email address
my app

You could model your authentication after the re-entry code system used at, where users' re-entry codes are generated randomly when they connect, unless they provide the re-entry code from their prior sessions.

Each phone could save the re-entry code in TinyDB, for convenience, to save having to re-type it each session.

The re-entry code would have to be used as part of the key of each user's data, in whatever server storage system you use.

thanks a lot..
i try also to use this extension