Install the index-opensearch.jar into the $GERRIT_SITE/lib directory.
Add the index-opensearch module to $GERRIT_SITE/etc/gerrit.config as follows:
[gerrit] installIndexModule = com.google.gerrit.opensearch.OpenSearchIndexModule
When installing the module on Gerrit replicas, use following example:
[gerrit] installIndexModule = com.google.gerrit.opensearch.ReplicaOpenSearchIndexModule
For further information and supported options, refer to config documentation.