There are several options. If you want to be able to modify the database from both Derby and MS-Access, then you will need to locate an ODBC driver for MS-Access that would enable it to read and modify a Derby database. Off hand, I do not know if such a driver exists.
If you wish to simply convert the database to an MS-Access format, then ...
... much will depend on the structure of the underlying tables and how much of the schema you need to preserve.
The simplest thing would be that you have a database consisting of a single table that resembles a flat-file database. In this case, you can write a simple JDBC tool to write your database out as a CSV file (for example) that MS-Access can read.
If you have multiple tables or data that can't be easily represented by a CSV file, then things become more complex. You haven't told us anything about your needs or the structure of your database, so it is unlikely that anyone can be more specific.