This article helps you how to reindex the Solr index used by AEM Communities MSRP and DSRP.
For MSRP Solr reindexing, see this documentation.
For DSRP you would follow the same steps but use this URL instead: /services/social/datastore/rdb/reindex
For example, your curl command for reindex on DSRP would look like this:
curl -u admin:password -X POST -F path=/ http://host:port/services/social/datastore/rdb/reindex