To modify an index, run the dsconfig tool. Any modification or addition of an index requires rebuilding the indexes. In general, an index only needs to be built once after it has been added to the configuration.
Note:
If you add an index and then import the data using the import-ldif tool, the index is automatically rebuilt. If you add an index and then add the data using a different method, you must rebuild the index using the rebuild-index tool.