T3 use Android operating system and now only works with sony reading software. It has not been rooted to enable access to aps store with different ereader aps. Sony tries hard to prevent this. Maybe it will require giving a top hacker a new T3 too make it happen.
Sony development forum should have thread covering any news if someone is rooting T3.
https://www.mobileread.com/forums/forumdisplay.php?f=141