Update faq.md

add FAQ for when the cluster identity changes

Author: frantran

articles/kubernetes-fleet/faq.md

@@ -45,6 +45,12 @@ The current preview of Azure Kubernetes Fleet Manager resource supports joining
 
 Azure Kubernetes Fleet Manager resource is a regional resource. Support for region failover for disaster recovery use cases is in the [roadmap](https://aka.ms/fleet/roadmap).
 
+## What happens when the user changes the cluster identity of a joined cluster?
+The member agent will automatically pick up the new identity and communicate with the hub using the new token.  \
+However, the fleet hub is unaware of the new identity, and needs to be reconfigured to authorize the member. \
+You can join the member cluster to the fleet again by performing a PutMember operation to notify the fleet hub to pick up the new identity. \ 
+If using Azure CLI, you can run "az fleet member create".
+
 ## Roadmap
 
 The roadmap for Azure Kubernetes Fleet Manager resource is available [here](https://aka.ms/fleet/roadmap).