To convert accdb to sqlite, i.e. MS Access databases to SQlite format, you will need a special database management tools that support import of Access databases and write data to SQLite database file format. You can also use some exchange data formats and export accdb files into csv or xml, sql and then import it to SQLite database.
On Windows, Mac and Linux systems you can use Navicat database management tools like Navicat for SQLite or Navicat Premium to same purposes. Navicat software is available for Mac OS.
Another alternative presents itself with utilities like the ACCDB MDB Explorer, or Access Database Manager for Mac or similar that can also transform Microsoft Access database files (.accdb) to SQLite database file format (.sqlite).