Thanks for using Wazuh.
Unfortunately, I didn't completely understand your question.
I think that what you are looking for is the
wazuh.yml file, used to configure the Wazuh plugin, the connection with the Wazuh APIs and the extensions of the app. These extensions are part of the Wazuh plugin, not custom dashboards. I don't know what you mean by custom dashboards. The location of the file is present in the link above.
Finally, the description of your environment is misleading. Kibana and OpenSearch are not compatible, so you are either using Elastic + Kibana or Wazuh Indexer + Wazuh Dashboard (based on OpenSearch and OpenSearch Dashboards respectively).
You are most likely using the latest, so the path to the file is:
/usr/share/wazuh-dashboard/data/wazuh/config/wazuh.ymlPlease, let me know if this was useful.