If you previously used XML based user repository you can import all data into MySQL database using repository management tool. This is quite long command so let me list all required parameters first with brief explanation:
And now whole command. Enter all in one line:
$ ./scripts/repo.sh -cp -sc tigase.db.xml.XMLRepository -su user-repository.xml -dc tigase.db.jdbc.JDBCRepository -du "jdbc:mysql://localhost/tigase?user=dbuser&password=dbpass"
For more information how to use command line administration tools refer to ////<<commandLineTools2,////command line tools guide.