Is there any specifig reason you're attempting to use Elastalert?
You see, Wazuh Dashboard (which is a fork of Opensearch Dashboard) includes Opensearch's Alerting module
that is fully compatible with Wazuh alerts.
Also, Wazuh includes its own integration module
that allows you to send alerts to external APIs defining a criteria to filter them. In case you're new to Elastalert, I do recommend you to check any of these commented methods.
Now, If you still want to proceed using Elastalert, then are you getting any specific error? Can you provide some screenshot of it? Any additional information will be usefult.
Looking forward to your comments.