File signature for .db file needed after failed restore
The format of these files is described in SQLite's documentation.

The db file is the main database and starts with the string "SQLite format 3\000" (note that \000 is the zero byte or ASCII NUL).

The db-journal file is the journal for the database. You only need it if the database was open when you performed the factory reset (that is, if the app was running and in the middle of writing the database). It starts with the following bytes: 0xd9, 0xd5, 0x05, 0xf9, 0x20, 0xa1, 0x63, 0xd7.